What is Rh factor

Rh factor also called Rhesus factor is a protein (a type of antigen) that’s found on some people’s red blood cells. The Rh blood group system also known as the Rhesus blood group system has over 50 Rh antigens; the 5 most significant Rh antigens are D, C, c, E, and e ¹, ², ³. Blood is either Rh-positive or Rh-negative. If your red blood cells have the Rhesus D protein (RhD antigen), you’re Rh-positive (Rh+). If your red blood cells don’t have the Rhesus D protein (RhD-), you’re Rh-negative (Rh-) ⁴,  ⁵, ⁶. Being Rh-positive or Rh-negative doesn’t affect your health. But it can affect your baby during pregnancy if you’re Rh-negative and your baby is Rh-positive. In addition, Rh factor is also important when you have a blood transfusion. It is important to be given the right blood when you have a blood transfusion. Blood comes in 4 main blood types: A, B, AB, and O. These types refer to molecules called antigens on the surface of your red blood cells, where they serve as built-in protection devices for your blood supply. Antigens that reside on the surface of your red blood cells are designed to identify foreign cells and trigger immune responses that produce antibodies in the plasma to attack potential foreign invaders. Antigens are substances that can cause a person’s immune system to react.

The Rh blood group system was first described in 1939 by Levine and Stetson ⁷ who described a pregnant woman that had postpartum hemorrhage and the woman developed a severe transfusion reaction when she was transfused with blood from her husband following delivery of a stillborn child with erythroblastosis fetalis or immune hydrops fetalis (this occurs when the mother’s immune system attacks the blood cells of the baby). Even though she and her husband were ABO compatible, she developed pain and discolored urine after the blood transfusion. Agglutination occurred when her blood was remixed with her husband’s blood and from 80% of Caucasian ABO-compatible donors ⁸, ⁷. Levine and Stetson tested her blood with multiple ABO-matched donors and noted agglutination with 80% of the donor samples. The authors concluded that the patient had been isoimmunized with an unknown antigen from her fetus resulting in the incompatible blood transfusion ⁸, ⁷.

The following year, Landsteiner and Wiener found that sera from rabbits and later guinea pigs immunized with red blood cells from Macaca mulatta (Macacus rhesus in the original paper) agglutinated 85% of human red blood cell samples. Initially, it was thought that the animal and human antibodies identified a common factor, Rhesus (Rh) factor, on the surface of rhesus monkey and human red blood cells ⁹. Landsteiner and Wiener work would also describe the autosomal dominant inheritance pattern of the Rh factor ¹⁰. Later, it was discovered that humans and rhesus monkeys do not share the same red blood cell antigens, though the name persists ¹¹. Therefore, the original terms Rh factor and anti-Rh coined by Landsteiner and Wiener, although being misnomers, have continued in common usage ². The heteroantibody was renamed anti-LW (after Landsteiner and Wiener), and the human anti-Rh antibody was renamed anti-D ¹²

You can find out if you’re Rh-positive or Rh-negative with a blood test. Most people in the United States are Rh-positive. If you’re Rh-negative, your partner can get tested to find out his Rh type.

The Rh blood group is encoded by two tightly linked loci on chromosome 1p34-36 (short arm of chromosome 1) ⁴. The RHD gene encodes the RhD antigen, and the RHCE gene encodes RhCE antigens. SMP1, a sequence of unknown significance, separates RHD and RHCE ¹³. RHD and RHCE encode eight haplotypes of the Rh antigens in various combinations. The Rh proteins are hydrophobic transmembrane proteins embedded in the red blood cell phospholipid bilayer with an extracellular expression of the antigens. Interestingly, the RhD and RhCE proteins are very similar, with the first 41 amino acids identical ¹⁴.

Rh factor is inherited. This means Rh factor is passed from parents to children through genes. Genes are parts of your body’s cells that store instructions for the way your body grows and works. A baby may inherit the Rh-factor from either parent or a combination of both. Unlike antibodies to A and B antigens that determines the ABO blood type, antibodies to Rh factor are not produced naturally. Antibodies that are produced against the Rh factor can develop only if you lack the Rh factor on your red blood cells and then you are exposed to Rh-positive red blood cells. This can happen during pregnancy or birth when the mother is Rh-negative and the baby is Rh-positive, or sometimes when you are Rh-negative and are transfused with Rh-positive blood. In either case, the first exposure to the Rh antigen may not result in a strong response against the Rh-positive cells, but any subsequent exposure such as a second pregnancy may cause severe reactions. These antibodies can cross the placenta and destroy your baby’s red blood cells, resulting in hemolytic disease of the fetus and newborn (an immune-mediated red blood cell disorder in which maternal antibodies attack fetal or newborn red blood cells) ¹⁵. All newborn babies of Rh-negative mothers are typed for ABO and Rh soon after birth. This determines if the mother needs to receive Rh immune globulin, which prevents her from developing Rh antibodies against her fetus’ blood cells. If a Rh-negative mother has a negative red blood cell Rh antibody screen, then an Rh immune globulin injection is given within 72 hours to prevent Rh antibody production. If she has a positive test, then the antibody or antibodies present must be identified. If an antibody to the D antigen has been actively formed by the mother, then the Rh immune globulin injection is not useful. If she has a different antibody, then the Rh immune globulin injection can still be given to prevent her from producing antibodies to the D antigen.

Rh disease also called Rh incompatibility happens when your blood is Rh-negative and your baby’s blood is Rh-positive ¹⁶. This means your blood and your baby’s blood are incompatible, so it’s not safe for them to mix together. If they do mix, your body makes Rh antibodies that may go from your body through the placenta into your baby’s body, where they attack and destroy your baby’s red blood cells. The placenta grows in your uterus (womb) and supplies your baby with food and oxygen through the umbilical cord.

Rh disease can cause serious problems for your baby, including:

• Anemia
• Brain damage
• Heart failure
• Jaundice. Jaundice can make your baby’s eyes and skin look yellow. A baby has jaundice when his liver isn’t fully developed or isn’t working. If jaundice is severe and isn’t treated, a baby can develop a kind of brain damage called kernicterus.
• Stillbirth. Stillbirth is when a baby dies in the womb after 20 weeks of pregnancy.
• Death after birth

The presence or absence of antigens on your red blood cells and corresponding antibodies in your plasma defines your ABO blood group.

Each person’s blood is one of 8 specific types:

• A+ (A Rh-positive) means your blood has A antigens and B antibodies and Rh protein,
• A− (A Rh-negative) means your blood has A antigens and B antibodies and no Rh protein,
• B+ (B Rh-positive) means your blood has B antigens and A antibodies and Rh protein,
• B− (B Rh-negative) means your blood has B antigens and A antibodies and no Rh protein,
• AB+ (AB Rh-positive) means your blood has A antigen and B antigen and Rh protein and no A and B antibodies,
• AB− (AB Rh-negative) means your blood has A antigen and B antigen and no A and B antibodies and no Rh protein,
• O+ (O Rh-positive) means your blood has no A antigen and no B antigen, but it has both A and B antibodies and Rh protein,
• O− (O Rh-negative) means your blood has no A antigen and no B antigen and no Rh protein, but it has both A and B antibodies.

Note: Not everyone has one of the 8 common blood types, as there are over 600 other antigens can reside on red blood cells, leading to countless rare blood types ¹⁷. Since blood type is hereditary (passed from parents to children through genes), rare blood types typically exist in ethnic groups, but you won’t usually know this until you experience a medical emergency.

The following table indicates the type of antibodies you are expected to have based on your blood type.

Table 1. ABO Blood Group System

Blood Type	Have Antibodies to
A	B antigen
B	A antigen
AB	No A and B antibodies
O	A and B antigens

Blood is categorized in four primary types, or groups, based off of the ABO system. The four potential blood types are A, B, AB, and O. Antigens that are on the surface of red blood cells are either type A or they are type B. Their presence, or absence, determines whether blood is a type A or B. Blood groups are determined based on these antigens. Each blood type contains a delicate balance of antigens and antibodies, and not all blood types are compatible with one another. Since antibodies are designed to fight corresponding antigens, a transfusion that mixes two incompatible blood types could cause the antibodies in one to attack the antigens in another. These antibody attacks can lead to the creation of clumps of red blood cells also known as agglutination. Agglutination can create blood clots, stop circulation, and may cause red blood cells to split and leak, which triggers toxic reactions.

Since mixing incompatible types can be harmful or even fatal, understanding your blood type is critical, especially if you’re donating blood or receiving a transfusion from a donor. After all, some blood types can’t pair safely with others, while others are compatible with several other types.

People with O− (O Rh-negative) blood do not have A, B, or Rh proteins (antigens) on their blood cells. These people can donate blood to anyone, and are known as universal donors (universal red cell donor). This means that a person that is O negative can donate his blood to anyone regardless of that person’s blood type. In an emergency or if your life is in danger, medical personnel will most commonly administer O- (O Rh-negative) blood. However, despite type O- (O Rh-negative) blood reputation as a universal donor option, even O- (O Rh-negative) blood may have antibodies that react with other types. Since even O- (O Rh-negative) blood can cause complications that increase the risk of blood transfusion, medical personnel typically strive to use blood that precisely matches that of the patient.

People who are AB+ (AB Rh-positive) have all three antigens (A, B, and Rh factor) on their blood cells and can safely receive blood from anyone. Type AB+ (AB Rh-positive) is the universal plasma donor. This means that a person with AB+ (AB Rh-positive) blood type can donate plasma to anyone.

Other blood types can donate and give to only their matching blood types.

If a person receives the wrong type of blood, his or her immune system will react to it. This is a serious condition that can cause severe symptoms such as fever, muscles aches, and trouble breathing. It can sometimes be fatal.

The 8 standard blood groups can pair as follows:

• Type A+ (A Rh-positive): Can donate blood to types A+ and AB+. Can receive blood donations from types A+, A-, O+, and O-.
• Type A- (A Rh-negative): Can donate blood to types A+, A-, AB+, and AB-. Can receive blood donations from types A- and O-.
• Type B+ (B Rh-positive): Can donate blood to types B+ and AB+. Can receive blood donations from types B+, B-, O+, and O-.
• Type B− (B Rh-negative): Can donate blood to types B+, B-, AB+, and AB-. Can receive blood donations from types B- and O-.
• Type AB+ (AB Rh-positive): Can donate blood to type AB+. Can receive blood donations from all eight types.
• Type AB− (AB Rh-negative): Can donate blood to types AB+ and AB-. Can receive blood donations from types AB-, A-, B-, and O-.
• Type O+ (O Rh-positive): Can donate blood to types O+, A+, B+, and AB+. Can receive blood donations from types O+ and O-.
• Type O− (O Rh-negative): Can donate blood to all eight types. These people can donate blood to anyone, and are known as universal donors (universal red cell donor). But can receive blood donations only from type O-.

Overall, types O+ (O Rh-positive) with 37 percent of the population and A+ (A Rh-positive) 36 percent of the population are by far the most common blood types in the United States. Almost 9% of Americans have either type B+ (B Rh-positive) or O− (O Rh-negative) blood, while 6% have type A- (A Rh-negative), and 3% have type AB+ (AB Rh-positive) blood. Types B− (B Rh-negative) and AB− (AB Rh-negative) are the least common in the U.S., appearing in 2% and less than 1% of the population, respectively.

The following table shows what types of blood patients can safely receive, based on their individual blood types.

Blood Group and Rh Type of Patient	Safe (Compatible) Blood Types for Red Blood Cell Transfusion*
A positive (A Rh-positive)	A positive, A negative, O positive, O negative
A negative (A Rh-negative)	A negative, O negative
B positive (B Rh-positive)	B positive, B negative, O positive, O negative
B negative (B Rh-negative)	B negative, O negative
AB positive (AB Rh-positive)	AB positive, AB negative, A positive, A negative, B positive, B negative, O positive, O negative
AB negative (AB Rh-negative)	AB negative, A negative, B negative, O negative
O positive (O Rh-positive)	O positive, O negative
O negative (O Rh-negative)	O negative

Footnote: * These apply for red blood cell transfusions only; when transfusing plasma products and platelets, the compatible choices are different.

A blood transfusion is when blood is put into your body. Your blood has several parts. Plasma is the liquid part of your blood. It’s made of water, proteins, clotting factors, hormones, salts and other substances. Floating in the plasma are many red blood cells that transport oxygen, white blood cells that combat infections, and platelets that aid in clotting when you’re injured. Red blood cells contain hemoglobin (Hb) and hemoglobin (Hb) lets red blood cells carry oxygen from your lungs to the rest of your body. Your whole body needs oxygen, so it’s important to have enough red blood cells. Your blood also contains white blood cells. These help the body fight infection. And your blood contains smaller cells called platelets. These help the blood clot. Proteins called clotting factors also help your blood clot. Without these, your body can’t stop bleeding from even a tiny wound.

Whole blood refers to blood with all these parts. Most of the time, a blood transfusion is done with only part of the blood. You might be given one or more of these blood parts based on your needs.

Whether you receive O− (O Rh-negative) blood or your exact match, physicians generally begin the transfusion process by testing compatibility. Carefully cross-matching a small sample of your blood with the donor’s blood ensures that the two are compatible and won’t cause additional complications.

Who gets tested for Rh factor?

You, your partner and your baby can have tests to find out if you’re Rh-positive (Rh+) or Rh-negative (Rh-) and if your baby is at risk for Rh disease. If you and your baby have the same Rh factor, your blood types are considered compatible and won’t cause problems. However, if you are Rh-negative and your partner has Rh-positive, there’s a chance your baby has a negative Rh factor, which could lead to complications. While your blood won’t normally come into contact with your baby’s blood, the two could mix during delivery or if trauma occurs at any time during your pregnancy. Because Rh factor is an antigen, it can elicit an immune response and you could develop antibodies against the Rh antigen. These antibodies can cross the placenta and destroy your baby’s red blood cells, resulting in hemolytic disease of the fetus and newborn (an immune-mediated red blood cell disorder in which maternal antibodies attack fetal or newborn red blood cells) ¹⁵.

You should get a blood test at your first prenatal care visit to find out if you’re Rh-positive or Rh-negative. If you’re Rh-positive, there’s no risk of Rh disease in your baby.

If you’re Rh-negative:

• You get a test called an antibody screen to see if you have Rh antibodies in your blood.
• If you don’t have Rh antibodies, your partner gets tested to see if he’s Rh-positive or Rh-negative.
• If your partner is Rh-positive (Rh+) or you don’t know your partner’s Rh factor, your doctor may recommend an amniocentesis to check your baby’s Rh factor or his bilirubin level. Bilirubin is a yellow substance that can build up in your baby’s blood when his liver isn’t working right. You get a second antibody test at 28 weeks of pregnancy. If this second test shows that your baby has anemia, your doctor may do a Doppler ultrasound to check the flow of blood into your baby’s head.
• In the event that your blood do mix with your baby’s blood, your red blood cells could begin to produce Rh antibodies. While these antibodies aren’t likely to cause harm to you or your baby right away, they could affect your next pregnancy. During your next pregnancy, there’s a chance that the Rh antibodies could enter your baby’s blood supply. If you’re Rh-negative and your baby is Rh-positive, the antibodies could attack your baby’s red blood cells and cause anemia, a condition that could be fatal to your unborn child. To combat these potential complications, doctors often recommend that Rh-negative mothers have a blood test to screen for Rh antibodies during the first trimester and again at delivery. If you test positive for Rh antibodies at your 28th week of pregnancy, your obstetrician will generally monitor you and your baby carefully, providing a blood transfusion for the baby if necessary.
• If the Rh antibody test you take in your first trimester produces a negative result, you’ll typically receive an Rh immune globulin injection called Rho(D) immune globulin (brand name RhoGAM) to prevent your blood cells from generating any antibodies throughout your pregnancy. Rho(D) immune globulin consists of anti-Rh D antibodies that target Rh-positive red blood cells to prevent maternal sensitization. Rh immune globulin injection can prevent your body from producing Rh antibodies so your baby and future pregnancies won’t get Rh disease. Rh immune globulin injection doesn’t work if your body has already started making Rh antibodies in a previous pregnancy. This is why it’s really important to get prenatal care as early as possible in every pregnancy.
• You’ll undergo another blood test at delivery. If your baby is born Rh-positive (Rh+), you’ll typically need a second injection, but if your baby is born Rh-negative (Rh-), you won’t usually need additional treatment. In some cases, you’ll need additional injections to protect yourself and any future children. Prenatal tests like amniocentesis, chorionic villus sampling, or cordocentesis can all cause your baby’s blood to mix with yours and may require an injection. If you experience a miscarriage, an ectopic pregnancy, substantial bleeding, or an abortion, Rh immune globulin is typically necessary.

If I’m Rh-negative, can I protect my baby from Rh disease?

Rh disease can be prevented in your baby if you get treatment at the right times. If you haven’t developed Rh antibodies, your doctor can give you a shot of Rh immunoglobulin called Rho(D) immune globulin (RhoGAM). Rh immune globulin injection can prevent your body from producing Rh antibodies so your baby and future pregnancies won’t get Rh disease. Rh immune globulin injection doesn’t work if your body has already started making Rh antibodies in a previous pregnancy. This is why it’s really important to get prenatal care as early as possible in every pregnancy.

If you’re Rh-negative, you get Rh immune globulin injection:

• At about 28 weeks of pregnancy
• Within 72 hours after the birth if your baby is Rh-positive or if his Rh is unknown
• After any situation in which your blood and your baby’s blood may mix, like amniocentesis or chorionic villus sampling, miscarriage, ectopic pregnancy or a hit to your belly.

Your provider watches your baby closely during pregnancy to check his health and for signs of anemia. In your third trimester, your doctor may use amniocentesis or a special ultrasound called Doppler to check your baby. Ultrasound is a prenatal test that uses sound waves and a computer screen to show a picture of your baby inside the womb. A Doppler ultrasound helps a provider check your baby’s heartbeat and measure the blood flow in the umbilical cord and certain blood vessels.

If my baby has Rh disease, how she/he is treated?

If your baby has Rh disease, she can be treated to help prevent serious health problems.

If your baby has mild Rh disease, you may be able to have a full-term pregnancy. Full term means your baby is born between 39 weeks and 40 weeks, 6 days. After birth, your baby may need certain medicine, and she may need treatment for jaundice. Sometimes Rh disease is so mild that your baby doesn’t need any treatment. Most babies recover fully from mild Rh disease.

If your baby develops severe Rh disease and severe anemia before birth, you may have to give birth early, before her due date. She may need a blood transfusion with new blood to replace red blood cells that the Rh antibodies destroyed. Babies can get a blood transfusion in the womb as early as 18 weeks of pregnancy; they also can get a transfusion after birth.

If your baby is born with severe jaundice, she needs quick treatment to prevent more serious complications.

What happened before the Rh immune globulin injection was developed?

Prior to development of the Rh immune globulin injection, Rh-negative mothers would often become sensitized from the blood of their first Rh-positive baby and begin developing anti-Rh antibodies. Any subsequent Rh-positive babies would have some degree of Rh disease, due to the mother’s anti-Rh antibodies attacking the baby’s red blood cells. Miscarriages and stillborn babies were relatively common, and those babies who were born often needed immediate blood transfusions to survive. The Rh immune globulin injection has largely prevented these complications, although a small percent of women do still develop Rh antibodies.

What is hemolytic disease of the newborn?

Hemolytic disease of the newborn (HDN) also called immune erythroblastosis fetalis, ABO incompatibility HDN or Rh incompatibility HDN, is a potentially life-threatening condition that occurs when the blood types of a mother and baby are incompatible. Hemolytic disease of the newborn results from maternal antibodies attacking fetal red blood cells due to incompatibility of maternal and fetal blood based on the Rhesus (Rh) and ABO antigen systems where antibodies from a Rhesus negative (Rh-) pregnant mother attack a Rhesus positive (Rh+) fetus ¹⁸. Hemolytic disease of the newborn or erythroblastosis fetalis can destroy the newborn baby’s blood cells very quickly, which can cause symptoms during pregnancy or after the baby is born. The severity of hemolytic disease of the newborn can vary. Each child may experience different symptoms of hemolytic disease of the newborn (erythroblastosis fetalis). Some babies have no symptoms. In other cases, problems such as hydrops can cause the baby to die before, or shortly after, birth. Severe hemolytic disease of the newborn (erythroblastosis fetalis) may be treated before birth by intrauterine blood transfusions.

The most common symptoms of hemolytic disease of the newborn (erythroblastosis fetalis) are:

• pale skin
• yellowing of the amniotic fluid, umbilical cord, skin, and eyes (jaundice)
• enlarged liver or spleen
• severe swelling of the body (edema)

During pregnancy, symptoms of hemolytic disease of the newborn or immune erythroblastosis fetalis may include:

• Large amounts of amniotic fluid
• Thickened placenta
• Enlarged liver, spleen, or heart in the baby
• Fluid buildup in the baby’s abdomen
• Mild anemia: When the baby’s red blood cell count is deficient, his blood cannot carry enough oxygen from the lungs to all parts of his body, causing his organs and tissues to struggle.
• Hyperbilirubinemia and jaundice: The breakdown of red blood cells produces bilirubin, a brownish yellow substance that is difficult for a baby to discharge and can build up in his blood (hyperbilirubinemia) and make his skin appear yellow.
• Severe anemia with enlargement of the liver and spleen: The baby’s body tries to compensate for the breakdown of red blood cells by making more of them very quickly in the liver and spleen, which causes the organs to get bigger. These new red blood cells are often immature and unable to function completely, leading to severe anemia.
• Hydrops fetalis: When the baby’s body cannot cope with the anemia, his heart begins to fail and large amounts of fluid buildup in his tissues and organs. Hydrops (fluid throughout the body’s tissues, including in the spaces containing the lungs, heart, and abdominal organs), which can lead to heart failure or respiratory failure from too much fluid.

After birth, symptoms of hemolytic disease of the newborn or immune erythroblastosis fetalis may include:

• Pale coloring
• Severe swelling overall (edema), especially in the baby’s abdomen
• Enlarged liver and spleen
• Difficulty breathing
• Severe hyperbilirubinemia and newborn jaundice which occurs sooner and is more severe than normal. Excessive buildup of bilirubin in the baby’s blood causes his liver to become enlarged.
• Kernicterus: Buildup of bilirubin in the blood is so high that it spills over into the brain, which can lead to permanent brain damage.

Hemolytic disease of the newborn is currently estimated to affect 3 to 8 of every 100,000 pregnancies ¹⁹. The occurrence of hemolytic disease of the newborn is directly correlated with the inheritance pattern in females that results in the absence of the Rhesus (D) antigen; however, the incidence of hemolytic disease of the newborn is seen to vary with ethnicity ²⁰. For instance, it has been found that whites have the highest prevalence of hemolytic disease of the newborn, and Asians and American Indians have the lowest, as illustrated in Table 3 below. Furthermore, among the Rh antigens in existence, the most immunogenic one is the D antigen. It is approximated that about 10% of pregnant white women are Rh incompatible ¹⁸.

Table 3. Prevalence of hemolytic disease of the newborn according to ethnic groups

Ethnicity	Prevalence of hemolytic disease of the newborn by percentage
Africans	4%
African-Americans	8%
Whites	15–16%
Eurasians	2.4%
Asians	<1%
Basque (Spain/France)	30–35%

[Source ¹⁸ ]

Hemolytic disease of the newborn is preventable. Before the onset of Rh immunoglobulin therapies, 1% of all pregnancies resulted in fetal death from hemolytic disease of the newborn. Today, nearly all women with Rh-negative blood are identified in early pregnancy through blood tests. If a mother is Rh-negative and has not been sensitized, she is usually given a drug called Rh immunoglobulin or RhoGAM. This specially developed blood product prevents an Rh-negative mother’s antibodies from reacting to her baby’s Rh-positive red blood cells. Mothers are typically given RhoGAM around the 28th week of pregnancy and again within 72 hours of giving birth.

Typically, it is the second Rh-positive fetus that is affected. When the first child inherits the father’s D antigen, whose inheritance has been shown to follow an autosomal dominant pattern, and maternal and fetal blood mixing occurs during the pregnancy. This mixing most commonly happens during labor and delivery but can theoretically occur at any time during the pregnancy. Once maternal and fetal blood mixing occurs during the pregnancy, pregnant mother begins producing anti-D antibodies. This constitutes alloimmunization, as the pregnant mother is D-negative ²¹.

The initial antibodies produced are IgM, which cannot cross the placental barrier. However, when isotype switching occurs, IgG antibodies are produced. IgG antibodies can cross the placental barrier, and they do so during the second and or subsequent pregnancies, attacking the fetal red blood cells and causing hemolysis and associated complications such as hydrops fetalis and jaundice ²². Although, the IgG antibodies can enter fetal circulation through fetomaternal hemorrhage as well.

The general absence of maternal and fetal blood mixing during the first pregnancy and the delay of IgG antibody production make it unlikely that the first D-negative pregnancy is affected. However, in the subsequent D-negative pregnancy, IgG antibodies cross the placenta and attack the D antigens on fetal red blood cells. This leads to hemolysis that may result in jaundice, anemia, kernicterus, and hydrops fetalis. Intrauterine death may occur without intrauterine blood transfusion, and any surviving fetus may have developmental delays, hearing loss, and hypotonia ¹⁸.

Hemolytic disease of the newborn can be diagnosed during pregnancy or after the baby is born. Tests conducted during pregnancy may include:

• complete blood count test for the mother
• ultrasound
• amniocentesis
• cordocentesis

After birth, tests may include:

• complete blood count test for the baby
• umbilical cord blood test

Hemolytic disease of the newborn can be treated during pregnancy or after the baby is born. Treatment during pregnancy may include:

• blood transfusion
• early delivery of the baby if severe complications arise and baby’s lungs are mature

After birth, treatment may include:

• Blood transfusion
• Intravenous fluids
• Oxygen or mechanical breathing machine
• Light therapy (phototherapy) using special blue lights to convert bilirubin into a form which is easier for the baby’s body to get rid of.
• Antibodies (intravenous immunoglobulin, or IVIG) to help protect the baby’s red cells from being destroyed.
• Feeding often and receiving extra fluids.
• Medicines to raise blood pressure if it drops too low.
• In severe cases, an exchange transfusion to replace the baby’s damaged blood with fresh blood may need to be performed. This involves removing a large amount of the baby’s blood, and thus the extra bilirubin and antibodies. Fresh donor blood is infused.
• Simple transfusion (without exchange). This may need to be repeated after the baby goes home from the hospital.

What is hemolytic transfusion reactions?

Hemolytic transfusion reactions are one possible complication from blood transfusions ²³, ²⁴. Hemolysis means rupture or destruction of red blood cells and leakage of their contents. The site of hemolysis can be intravascular (in circulation) or extravascular (in reticuloendothelial system) ²³. Hemolytic transfusion reactions can be immune or non-immune mediated ²⁵, ²⁶, ²⁷. Immune hemolytic transfusions reactions occur due to immunological mismatch or incompatibility between the red blood cells from the blood donor and the transfusion recipient, resulting in extravascular or intravascular immune-mediated hemolysis ²⁸. An intravascular hemolytic transfusion reaction is typically more clinically severe than extravascular hemolysis ²⁹. Hemolytic transfusion reactions, in general, occur most often after transfusion of packed red blood cells but they can also occur after transfusion of other blood products ³⁰, ³¹. Non-immune hemolysis can be due to thermal, osmotic, mechanical injury to red blood cells or other blood products. Human or machine error cause these forms of hemolysis.

Hemolytic transfusion reaction is rare, with an incidence of 1:70,000 per unit transfused ²⁸, ²³. Hemolytic transfusion reactions are classified by their severity and onset time, which are divided into acute versus delayed hemolytic reactions ²³. Acute hemolytic reactions happen within 24 hours of transfusion and delayed hemolytic reactions happen after 24 hours ²³. Delayed reactions usually occur two weeks after but can go up to 30 days post transfusion ²³.

Hemolytic transfusion reactions greatly vary in severity from mild, clinically insignificant hemolysis presenting weeks after the transfusion to very sudden and life-threatening intravascular hemolysis leading to shock, renal failure, disseminated intravascular coagulation (DIC), and death. The main determining factor of hemolytic transfusion reaction’s onset and severity is the antibody’s class, such as IgG, IgM, IgG subclass, or complement binding, the antigens targeted, and their titer concentration ³².

Classically, acute hemolytic transfusion reaction is described as a triad of symptoms; fever, flank pain, and red or brown urine. However, this classic presentation is not seen often ²³. Other symptoms are chills, hypotension, renal failure, back pain, or signs of disseminated intravascular coagulation (DIC) ²³. On a peripheral blood smear, signs are consistent with immune hemolysis such as keratocytes, helmet cells, bite cells, blister cells, spherocytes, or microsporocytes. There is urinary hemosiderin on urine analysis. Serum haptoglobin is low, lactate dehydrogenase and unconjugated bilirubin are high ²³.

Delayed transfusion reactions are usually insidious. Patients present late after transfusion, 24 hours to 30 days. The presenting symptom is usually jaundice or low-grade fever. Clinical labs look similar to those described above and are consistent with hemolysis.

Non-immune hemolysis patients present like acute hemolytic transfusion reaction patients.

The most severe type of hemolytic transfusion reaction occurs during an ABO mismatch, typically due to clerical error. Patients who create AB antigens do so because of molecular mimicry to antigen presentation of gastrointestinal bacteria. These antibodies are typically IgM but may also be IgG. Severe reactions occur when IgM binds to ABO-typed antigens on red blood cells and subsequently fixes complement, creating a sudden, massive intravascular rupture of red blood cells. Hemolysis releases large amounts of hemoglobin, resulting in shock, renal failure, and disseminated intravascular coagulation (DIC) leading to hemorrhage and hypercoagulability with thrombosis ⁴.

Extravascular hemolytic transfusion reactions occur when the antibody targeting the red blood cells results in opsonization. Opsonized cells are sequestered by the macrophages of the reticuloendothelial system, primarily in the liver and spleen. Extravascular hemolysis is a comparatively slower and more progressive process, as each red blood cell may make several passes through the reticuloendothelial system before being phagocytosed. Unlike intravascular hemolysis, the hemoglobin is released inside the sequestering macrophage, where it is processed normally. The clinical manifestations of extravascular hemolysis are typically milder, resulting in hyperbilirubinemia and fever. However, more severe complications, such as kidney failure, may also occur ²⁹.

Whenever a transfusion hemolytic reaction is suspected, immediately stop the transfusion. Check labels on the patient, blood components, and paper work to rule our clerical error, since this is the most common cause. Also check signs of machine/mechanical error like intravenous needle gauge size, any other fluids given to patient and temperature of blood to rule out non-immune causes of hemolysis. Repeat ABO testing on the post-transfusion patient sample. Repeat crossmatch with pre-and post-transfusion specimens using an indirect antiglobulin testing and do direct antiglobulin (Coombs) testing. Order a peripheral smear to look for signs of hemolysis. Trend complete blood counts to monitor the severity of hemolysis. Trend other hemolysis labs like bilirubin, haptoglobin, and lactate dehydrogenase. Coagulation studies to monitor for disseminated intravascular coagulation. Urinalysis and microscopy to monitor for hemoglobinuria. Basic metabolic panel to monitor for signs of renal failure. If ABO incompatibility is negative, then test for other antibodies.

Treatment for hemolytic transfusion reactions is mainly supportive care. Reactions can range from mild to severe. As mentioned before, the first step is always to stop the transfusion. If unsure of the diagnosis, then one should send the blood for testing as discussed previously. However, if clinical suspicion is high or symptoms are severe, e.g., hypotension, immediate resuscitation should be started. Ensure the patient has good intravenous access. Aggressive hydration is usually recommended with normal saline to maintain a urine output at least 1 ml/kg/hr. This is to reduce the likelihood of complications of free hemoglobin in the blood stream such as acute kidney injury or disseminated intravascular coagulation. Sometimes diuretics are used to achieve adequate urinary output. If the patient does have disseminated intravascular coagulation (DIC), it will also need to be managed with appropriate blood products ³³, ³⁴, ³⁵.

What is immune-mediated hemolytic anemia?

Immune-mediated hemolytic anemia occurs when autoantibodies bind to red blood cells, resulting in hemolysis and possible anemia. The autoantibodies are generally IgG, although IgM and IgA have also been reported ³⁶. Particular subclasses of antibodies are more destructive than others; IgG1 and IgG3 can fix complement at a high rate and are very destructive. The red blood cells are mainly cleared through the reticuloendothelial system, but intravascular hemolysis may occur in severe cases.

Like many autoimmune disorders, most immune-mediated hemolytic anemias are associated with an underlying or triggering condition. Common triggering conditions are viral infections, autoimmune disorders, immunodeficiency, or pregnancy. Rarer instances of medication interactions, spider bites, sickle cell disease, babesiosis, and organ transplants have been documented ³⁷.

What influences my blood type?

Blood type is a hereditary trait, it is passed from parents to children through genes and is determined by two factors: the ABO grouping system and the Rh factor, such that your parents’ blood types determine your blood type. While children’s blood types aren’t necessarily an exact match for one of their parents, understanding parents’ blood types can help narrow down the potential types that children could have.

A single gene determines ABO blood type, and three versions of the gene exist: A, B, and O. Both A and B versions of the blood type gene are dominant, and the O version is recessive. Children inherit one version of the gene from each parent, resulting in six potential combinations of genes that place them in one of four ABO groups.

For example, a child who inherits an A version of the gene from one parent and a B version from the other will have blood type AB. Inheriting an A version and an O version of the gene will result in blood type A, while inheriting two O versions of the gene will result in blood type O.

A separate gene determines whether children have the Rh factor. Since Rh factor is either positive or negative, only two versions of this gene exist. In this case, the positive version is dominant, and the negative version is recessive. That means inheriting a positive version and a negative version of the gene will result in blood type Rh-positive (Rh+), while inheriting two negative versions will result in blood type Rh-negative (Rh-).

Although creating a hereditary chart can help in assessing potential blood type options for current and future generations, this method isn’t scientific. Only a reliable test can confirm your blood type.

I’m blood type O. Do I have a chance of having a baby with ABO hemolytic disease of the newborn?

Yes. Hemolytic disease of the newborn may occur when there is an ABO incompatibility between mother and baby, especially with mothers who are blood group O. However, the red blood cell antibody screen is not useful in this situation because our bodies naturally produce antibodies against the A and B antigens we do not have on our red blood cells. A mother who is blood type A will naturally have antibodies directed against the B surface antigens on red blood cells, and a mother who is type B will have anti-A antibodies, and so on. Generally, this is a mild form that is easily treatable.

Rh Pathophysiology

Rh proteins require the presence of Rh-associated glycoprotein (RhAG) for proper assembly in the red blood cell membrane ³⁸. Though Rh-associated glycoprotein (RhAG) and the Rh proteins are similar in structure, the gene locus for RhAG is located on chromosome 6p12-21. The combination of the Rh proteins and Rh-associated glycoprotein (RhAG) is termed the Rh family. Various other accessory glycoproteins comprise the Rh structure, including LW glycoprotein, integrin-associated protein, glycophorin B, and band 3 glycoprotein, encoded on chromosomes 19, 3, 4, and 17, respectively ⁴. The Rh proteins, Rh-associated glycoprotein (RhAG), and accessory proteins are collectively termed the Rh complex ². The function of the Rh complex is unclear. Studies of different Rh phenotypes indicate that the Rh complex plays a role in the red blood cell membrane integrity and may be involved with ammonium transport across the red blood cell membrane ^{13 4}.

Various Rh complex phenotypes exist due to point and nonsense mutations, rearrangements, and nucleotide deletions. Of these phenotypes, a lack of D antigen (D-negative), weak D, partial D, RhCE variants, and Rhnull have clinical implications.

Lack of D Antigen

The lack of D antigen (D-negative) occurs for various reasons closely linked to ethnicity ²⁰. Commonly identified in White populations, the deletion of RHD or mutations resulting in a premature stop codon produces the D-negative phenotype. In other people, the lack of D-antigen may be due to mutations preventing gene expression. For example, in African populations, the presence of a pseudogene leads to base pair duplication preventing gene expression ¹³. Patients lacking D-antigen warrant special consideration to prevent alloimmunization (an immune response to foreign antigens after exposure to genetically different cells or tissues, most commonly occurring after pregnancy or blood transfusions); if exposed to D-antigen through blood transfusion or pregnancy, they may develop anti-D antibodies, as seen when a D-negative pregnant woman with a D-positive fetus ³⁹.

Weak D

Approximately 1% of D-positive individuals type as weak D (historically known as Du), characterized by weak or absent red blood cell agglutination by anti-D antibodies during routine serologic testing. In weak D individuals, the D antigen usually requires enhancement with anti-human globulin (AHG) owing to a quantitative decrease in RhD protein. The weak D phenotype is a quantitative change in the D-antigen epitope caused by a defect in transcribing the RHD gene ². Various weak D genotypes exist; Types 1, 2, and 3 are the most common and produce sufficient D antigen epitopes to be managed as D-positive ⁴⁰. Female patients of childbearing age who are positive for a weak D phenotype should undergo additional genotyping to determine if immunoprophylaxis during pregnancy is necessary ⁴¹.

Partial D

The partial D phenotype is a qualitative change to the D antigen epitope caused by RHD gene conversions, point mutations, or expression of a low-incidence antigen ¹³. The majority of patients with partial D phenotype will type D-positive. Notably, these patients may form anti-D antibodies if exposed to D-positive red blood cells and require special consideration for transfusion and during pregnancy ⁴⁰.

RhCE Variants

RhCE polymorphisms occur due to single or multiple nucleotide substitutions in RHCE. The E and e alleles differ only by a proline to alanine substitution. However, the C and c polymorphic alleles have four different amino acid substitutions ⁴². The expression of these different alleles significantly impacts patients receiving chronic transfusions as they may develop alloantibodies more frequently. Notably, patients with sickle cell disease are at particular risk for alloimmunization ⁴³.

Rhnull

Rhnull phenotype contains two classifications, amorph and regulator. Amorph Rhnull occurs from a mutation of RHCE, leading to nonfunctional proteins on a D-negative background. Regulator Rh-null is the most common phenotype due to an RHAG mutation that produces dysfunctional Rh-associated glycoprotein (RhAG) ¹³. Clinically, Rhnull patients have shortened red blood cell life spans, characteristic red blood cell morphology on a peripheral blood smear and compensated hemolytic anemias. Transfusion support can be challenging because Rhnull individuals can become sensitized to multiple Rh antigens, including high-frequency antigens. Some alloimmunized Rhnull patients can develop anti-RH29 antibodies; however, this antibody does not react with Rhnull red blood cells ⁴⁴.

Rh blood type testing procedures

Rh blood typing detects the presence or absence of the D antigen on the surface of red blood cells using an anti-D reagent and is performed at the same time with ABO typing ⁴⁵. D antigen positive is Rh-positive, and D antigen negative is Rh-negative.

During Rh typing, the red blood cells of the patient are combined with reagent anti-D antibodies, and the resulting presence or absence of agglutination confers the Rh “positive” or “negative” status, respectively ⁴⁶. While not routinely required for pretransfusion testing, serologic testing to detect weak D or partial D phenotypes should occur in cases of ambiguous Rh typing or discrepancies with a patient’s historical typing result ⁴⁷. In cases of an apparently negative Rh type, the serologic assessment for weak or partial D requires adding anti-human globulin (AHG) reagent to enhance otherwise undetectable agglutination. Agglutination in this context suggests the presence of a weak or partial D phenotype; definitive distinction requires subsequent molecular genotyping to predict the true D antigen phenotype ⁴⁸.

Various methods for Rh blood group testing may be employed. Serological testing is most commonly based on hemagglutination reactions with red blood cell antigens against specific antibodies ⁴⁵. The hemagglutination process occurs in 2 stages. The first stage, often called red blood cell sensitization, combines paratope and epitope in a reversible reaction that follows the law of mass action and has an associated equilibrium constant. Noncovalent attractions hold together the antigen and antibody. During the second stage, multiple red blood cells with bound antibodies form a stable latticework through antigen-antibody bridges formed between adjacent cells. This latticework is the basis of all visible agglutination reactions ⁴⁹.

Reagents that detect the D antigen in the slide, tube, microplate, automated, and gel tests often have different formulations and performance characteristics. Various anti-D reagents may contain different antibody clones, potentiators, additives, or diluents, and reagents that contain the same antibody clone may vary in antibody dilution or preservative. Hence, instructions for testing may differ and must be consulted and followed carefully for accurate testing ⁵⁰.

Diagnostic tests

The direct antiglobulin test (DAT) demonstrates the in vivo coating of red blood cell surfaces with immunoglobulin antibodies or complement protein C3. The direct antiglobulin test (DAT) is most commonly utilized for the serologic investigation of potential antibody-mediated hemolysis ⁵¹. Clinical situations warranting a direct antiglobulin test (DAT) include acute or delayed hemolytic transfusion reactions due to antibody incompatibility, hemolytic disease of the fetus and newborn, and antibody-mediated drug-induced hemolysis. While a direct antiglobulin test (DAT) is not routinely performed for otherwise uncomplicated pretransfusion testing, it may be informative in cases where the auto-control is reactive to confirm the presence of self-reactive antibodies ⁵².

The direct antiglobulin test (DAT) is performed by directly adding antihuman globulin (AHG) reagent to a sample of the patient’s red blood cells and observing for agglutination with a positive reaction occurring if the red blood cells are already coated such that anti-human globulin (AHG) can bind. All positive direct antiglobulin test (DAT) samples should be tested with an inert control such as saline or 6% albumin before concluding a direct antiglobulin test (DAT) test is positive ⁵¹. Various preparations of anti-human globulin (AHG) sera are available for blood bank testing; the choice of anti-human globulin (AHG) preparation is dictated by the application, direct or indirect, and whether testing is being performed to detect red blood cell sensitization by IgG, complement, or both ⁵³.

The indirect antiglobulin test (IAT) is performed to detect in vitro antibody binding to red blood cells, regardless of the antibody’s ability to fix complement. Laboratory indications include antibody detection as in crossmatch and antibody screening, antibody identification, antibody titration, and red blood cell phenotyping. Antiglobulin testing may be performed using test tubes, capillary tubes, microtiter plates, or gel microtube techniques ⁵⁴. To standardize antiglobulin sera and confirm true-negative antiglobulin reactions, two types of quality control red blood cells are customarily used, those coated with IgG and those coated with C3b, C3d, or both. Rh antibodies are usually used to sensitize red blood cells with IgG ⁵².

Quality control cells for the antiglobulin test are called check cells or Coombs control cells. In a true-negative test, free active antiglobulin reagent should remain. Control cells, sensitized with IgG or C3, are added to all negative tests and centrifuged. Hemagglutination of check cells confirms the presence and reactivity of the anti-human globulin (AHG) reagent, thus validating a negative test result. If the control cells fail to agglutinate in any tube, the tests must be repeated because they are invalid and may have yielded false-negative results ⁵⁵.

Although the antiglobulin test is extremely sensitive, a negative test does not exclude the possible presence of antibodies on red blood cells. A negative reaction can occur with small quantities of bound IgG and C3 ⁵¹. In addition, anti-human globulin (AHG) sera may possess greater activity against some subclasses of IgG than others. Consequently, certain anti-human globulin (AHG) sera may produce negative results with red blood cells coated by a particular IgG subclass ⁵⁶.

Slide Testing

A glass slide containing a drop of 40% to 50% serum or plasma suspension of red blood cells and a drop of anti-D is mixed and placed on a heated Rh viewing box tilted continuously for 2 minutes to observe for agglutination. To rapidly warm the materials on the slide at 37°C, the Rh viewing box is kept at a temperature between 40°C and 50°C. The result is positive when the patient sample shows agglutination and the control shows suspension ⁵⁷. The sensitivity of this method is low and can be easily affected by multiple factors, thus making standardization difficult ⁵⁸.

Tube Testing

The test tube method can be utilized for emergency and first-time blood group typing. The test tube method is quicker, more sensitive, and uses fewer reagants than the slide method ⁵⁷. In the test tube method, a patient’s antibody-containing plasma and reagent red blood cells known to express specific antigens are combined in a test tube. Alternatively, a patient’s red blood cells may be combined with reagent antibodies of known specificity. The mixture undergoes a series of centrifugation and incubation steps with stepwise quantitation of agglutination. The strongest agglutination, a 4+ reaction, results in an effectively nondissociable single clump of red blood cells when the tube is gently agitated, whereas the weakest agglutination, a negative reaction, results in complete dissociation into individual red blood cells by the same assessment. The intermediate strength reactions fall in a spectrum in between these extremes ⁵⁹.

Gel Testing

The gel testing method is a widely available alternative serologic testing method that utilizes dextran acrylamide gel-containing microtube columns built into small plastic cards ⁶⁰. Antibodies containing plasma and reagent red blood cells are combined in a chamber above the columns, and the card is subsequently centrifuged to force the red blood cells down through the permeable gel, which acts like a size-selective sieve. The gel is typically impregnated with anti-human globulin (AHG) to facilitate agglutination. Depending on the degree of agglutination, the red blood cells have varying mobility as they travel down the column, and their visible stopping point quantifies the reaction. Gel method testing can be automated and has the advantage of a more objective scale for quantifying results than tube testing ⁴⁵.

Microplate Agglutination Testing

The microplate technology uses automated platforms to detect serum antibodies and red blood cell surface antigens ⁴⁹. The reactants are centrifuged and incubated in microplates, and the ABO or Rh D blood type is read through an automated system. The antiserum must indicate that it is formulated for automation or microplate Rh testing and may require the blood to be collected in a specific anticoagulant ⁴⁵.

False positive or negative results

False positive or negative results can be caused by improper technique, contaminated materials, omission of reagents or antisera, delays in reading tests, inadequate incubation time and temperature, inappropriate centrifugation, inappropriate or prolonged storage of red cells, and autoantibodies ⁶¹.

A patient or donor red blood cell sample previously found to be positive but now determined to be negative, or vice versa, should always be investigated to rule out identification, clerical, or recording errors ⁶¹. A new sample should be obtained and tested. If the discrepancy is between current and historical test results, the difference may be due to the testing method employed, phase of testing (indirect antiglobulin test [IAT] or direct antiglobulin test [DAT]), type of reagent (polyclonal vs. monoclonal), or manufacturer ⁶². Different reagents often contain different antibody clones that may demonstrate varying reactions with red blood cells with weak or partial Rh antigens. Knowledge of the ethnicity of the donor or patient can be helpful when investigating a typing discrepancy because some partial and weak phenotypes are more common in a specific ethnic group. Typing with several reagents from different manufacturers may be helpful ⁶³.

Rh incompatibility

Rhesus (Rh) incompatibility happens when your blood is Rh-negative and your baby’s blood is Rh-positive. This means your blood and your baby’s blood are incompatible, so it’s not safe for them to mix together. If they do mix, your body makes Rh antibodies that may go from your body through the placenta into your baby’s body, where they attack and destroy her red blood cells. Rhesus (Rh) incompatibility is associated with the development of maternal Rh sensitization and hemolytic disease of the neonate ⁶⁴. Rh factor is a protein that’s found on some people’s red blood cells. If your red blood cells have the Rh D antigen, you’re Rh-positive. If your red blood cells don’t have the protein, you’re Rh-negative. Being Rh-positive or Rh-negative doesn’t affect your health. But it can affect your baby during pregnancy if you’re Rh-negative and your baby is Rh-positive. Rhesus (Rh) incompatibility becomes clinically significant if a mother that is Rh-negative becomes sensitized to the D antigen and subsequently, produces anti-D antibodies (i.e., alloimmunization) that can bind to and potentially lead to the destruction of Rh-positive erythrocytes. This is of particular concern if a Rh-negative mother is carrying a Rh-positive fetus, which can result in consequences along the spectrum of hemolytic disease of the neonate ranging from self-limited hemolytic anemia to severe hydrops fetalis.

You can find out if you’re Rh-positive or negative with a blood test. Most people in the United States are Rh-positive. If you’re Rh-negative, your partner can get tested to find out his Rh type. In the US, only 15% of the population lack the Rh erythrocyte surface antigen and are considered Rh-negative. The vast majority (85%) of individuals are considered Rh positive ⁶⁵. Approximately 15-20% of white patients, as opposed to 5-10% of black patients, have the Rh-negative blood type. Among individuals of Asian and American Indian descent, the incidence of Rh-negative blood type is less than 5%.

Rh sensitization occurs in approximately 1 per 1000 births to women who are Rh negative. The Southwest United States has an incidence approximately 1.5 times the national average, which likely is caused by immigration factors and limited access to medical care since blood typing is a routine part of prenatal care. Even so, only 17% of pregnant women with Rh-negative blood who are exposed to Rh-positive fetal blood cells ever develop Rh antibodies.

Rh factor is inherited. This means Rh factor is passed from parents to children through genes. Genes are parts of your body’s cells that store instructions for the way your body grows and works.

The placenta grows in your uterus (womb) and supplies your baby with food and oxygen through the umbilical cord.

Even though you and your baby don’t share blood, a small amount of your baby’s blood can mix with yours during pregnancy. This can happen if:

• Your baby’s blood crosses into your blood through the placenta.
• You have an amniocentesis (also called amnio) or chorionic villus sampling (also called CVS). These are prenatal tests that your health care provider may recommend during pregnancy.
• You have bleeding during pregnancy.
• Your baby’s in a breech position (feet-down instead of head-down) before labor and your provider tries to rotate (move) him around so he’s head-down.
• You get hit in the belly during pregnancy.
• You have a miscarriage or an ectopic pregnancy. A miscarriage is when a baby dies in the womb before 20 weeks of pregnancy. An ectopic pregnancy is when a fertilized egg implants itself outside of the uterus (womb) and begins to grow.

If you have Rh antibodies, you’re called Rh-sensitized.

Your baby is at risk for Rh disease only if you’re Rh-negative and your baby is Rh-positive. Your baby is Rh-positive depending on the blood of you and your baby’s father. Here’s how it works:

• If both you and your baby’s father are Rh-positive: Your baby’s blood is Rh-positive, and there’s no risk of Rh disease in your baby.
• If both you and your baby’s father are Rh-negative: Your baby’s blood is Rh-negative, and there’s no risk of Rh disease for your baby.
• If you’re Rh negative and your baby’s father is Rh-positive: Your baby’s blood may be Rh-positive. Your baby is at risk for Rh disease and needs to be checked closely.

Talk to your doctor about having your blood and your baby’s father’s blood tested to find out if your baby may be at risk.

If it’s your first pregnancy, your body usually doesn’t make enough Rh antibodies to harm your baby. But if you get pregnant again, your body produces more antibodies that can cause Rh disease in your baby.

One of the main principles of the management of Rh incompatibility is the prevention of maternal sensitization. Rh D immunoglobulin (brand name RhoGAM®) has made a significant impact on preventing Rh disease. Rho(D) immune globulin consists of anti-Rh D antibodies that target Rh-positive red blood cells to prevent maternal sensitization. It has reduced the rate of alloimmunization from 16% to less than 1%. Furthermore, Rh D immunoglobulin (RhoGAM®) immunoprophylaxis has decreased the prevalence of hemolytic disease of the newborn (HDN) attributed to anti-D antibodies to less than 1%.

If you’re Rh-negative, you get Rh D immunoglobulin (RhoGAM):

• At about 28 weeks of pregnancy
• Within 72 hours after the birth if your baby is Rh-positive or if his Rh is unknown
• After any situation in which your blood and your baby’s blood may mix, like amniocentesis or chorionic villus sampling, miscarriage, ectopic pregnancy or a hit to your belly.

Rh incompatibility causes

Rh incompatibility can occur by 2 main mechanisms. The most common type occurs when an Rh-negative pregnant mother is exposed to Rh-positive fetal red blood cells secondary to fetomaternal hemorrhage during the course of pregnancy from spontaneous or induced abortion, trauma ⁶⁶, invasive obstetric procedures, or normal delivery. Rh incompatibility can also occur when an Rh-negative female receives an Rh-positive blood transfusion. In part, this is the reason that blood banks prefer using blood type “O negative” or “type O, Rh negative,” as the universal donor type in emergency situations when there is no time to type and crossmatch blood.

Exposure to fetal Rh-positive blood:

• Delivery (i.e., vaginal, Cesarean section)
• Threatened miscarriage, miscarriage
• Antepartum hemorrhage (e.g., placenta previa, abruption, vasa previa, uterine rupture)
• Trauma
• External cephalic version
• Invasive procedures (e.g., chorionic villus sampling, amniocentesis)
• Ectopic Pregnancy
• Molar pregnancy

Nonfetal exposure to Rh-positive blood:

• Transfusion
• Bone marrow transplantation
• Needle-stick injury

The most common cause of Rh incompatibility is exposure from an Rh-negative mother by Rh-positive fetal blood during pregnancy or delivery. As a consequence, blood from the fetal circulation may leak into the maternal circulation, and, after a significant exposure, sensitization occurs leading to maternal antibody production against the foreign Rh antigen.

Once produced, maternal Rh immunoglobulin G (IgG) antibodies persist for life and may cross freely from the placenta to the fetal circulation, where they form antigen-antibody complexes with Rh-positive fetal erythrocytes and eventually are destroyed, resulting in a fetal alloimmune-induced hemolytic anemia ⁶⁷. Although the Rh blood group systems consist of many antigen subtypes (eg, D, C, c, E, e), the D antigen is the most immunogenic; therefore, it most commonly is involved in Rh incompatibility.

Recommendations for screening for Rh incompatibility are available from the US Preventive Services Task Force ⁶⁸.

Rh incompatibility pathophysiology

The amount of fetal blood necessary to produce Rh incompatibility varies. In one study, less than 1 mL of Rh-positive blood was shown to sensitize volunteers with Rh-negative blood. Conversely, other studies have suggested that 30% of persons with Rh-negative blood never develop Rh incompatibility, even when challenged with large volumes of Rh-positive blood. Once sensitized, it takes approximately one month for Rh antibodies in the maternal circulation to equilibrate in the fetal circulation. In 90% of cases, sensitization occurs during delivery. Therefore, most firstborn infants with Rh-positive blood type are not affected because the short period from first exposure of Rh-positive fetal erythrocytes to the birth of the infant is insufficient to produce a significant maternal IgG antibody response.

The risk and severity of sensitization response increases with each subsequent pregnancy involving a fetus with Rh-positive blood. In women who are prone to Rh incompatibility, the second pregnancy with an Rh-positive fetus often produces a mildly anemic infant, whereas succeeding pregnancies produce more seriously affected infants who ultimately may die in utero from massive antibody-induced hemolytic anemia.

Risk of sensitization depends largely upon the following 3 factors:

1. Volume of transplacental hemorrhage
2. Extent of the maternal immune response
3. Concurrent presence of ABO incompatibility

The incidence of Rh incompatibility in the Rh-negative mother who is also ABO incompatible is reduced dramatically to 1-2% and is believed to occur because the mother’s serum contains antibodies against the ABO blood group of the fetus. The few fetal red blood cells that are mixed with the maternal circulation are destroyed before Rh sensitization can proceed to a significant extent.

Rh incompatibility is only of medical concern for females who are pregnant or plan to have children in the future. Rh-positive antibodies circulating in the bloodstream of an Rh-negative woman otherwise have no adverse effects.

Rh incompatibility prevention

Rh incompatibility can be prevented in your baby if you get treatment at the right times. If you haven’t developed Rh antibodies, your provider can give you a shot of Rh immunoglobulin called Rho(D) immune globulin (brand name RhoGAM®). RhoGAM can prevent your body from producing Rh antibodies so your baby and future pregnancies won’t get Rh disease. RhoGAM doesn’t work if your body has already started making Rh antibodies in a previous pregnancy. This is why it’s really important to get prenatal care as early as possible in every pregnancy.

If you’re RH-negative, you get RhoGAM:

• At about 28 weeks of pregnancy
• Within 72 hours after the birth if your baby is Rh-positive or if his Rh is unknown
• After any situation in which your blood and your baby’s blood may mix, like amniocentesis or chorionic villus sampling (CVS), miscarriage, ectopic pregnancy or a hit to your belly.

Your doctor watches your baby closely during pregnancy to check his health and for signs of anemia. In your third trimester, your provider may use amnio or a special ultrasound called Doppler to check your baby. Ultrasound is a prenatal test that uses sound waves and a computer screen to show a picture of your baby inside the womb. A Doppler ultrasound helps a provider check your baby’s heartbeat and measure the blood flow in the umbilical cord and certain blood vessels.

Rh incompatibility symptoms

While Rh incompatibility does not typically lead to clinical signs and symptoms in the Rh-negative mother, the consequences on the Rh-positive fetus can be substantial. Rh disease also called Rh incompatibility is a dangerous kind of anemia. Anemia is when a person doesn’t have enough healthy red blood cells to carry oxygen to the rest of the body.

Rh incompatibility can cause serious problems for your baby, including:

• Anemia
• Brain damage
• Heart failure
• Jaundice. Jaundice can make your baby’s eyes and skin look yellow. A baby has jaundice when his liver isn’t fully developed or isn’t working. If jaundice is severe and isn’t treated, a baby can develop a kind of brain damage called kernicterus.
• Stillbirth. Stillbirth is when a baby dies in the womb after 20 weeks of pregnancy.
• Death after birth

During the course of Rh incompatibility, the fetus is primarily affected. The binding of maternal Rh antibodies produced after sensitization with fetal Rh-positive erythrocytes results in fetal autoimmune hemolysis. As a consequence, large amounts of bilirubin are produced from the breakdown of fetal hemoglobin and are transferred via the placenta to the mother where they are subsequently conjugated and excreted by the mother. However, once delivered, low levels of glucuronyl transferase in the infant preclude the conjugation of large amounts of bilirubin and may result in dangerously elevated levels of serum bilirubin and severe jaundice.

Mildly affected infants may have little or no anemia and may exhibit only hyperbilirubinemia secondary to the continuing hemolytic effect of Rh antibodies that have crossed the placenta.

Moderately affected infants may have a combination of anemia and hyperbilirubinemia/jaundice.

In severe cases of fetal hyperbilirubinemia, kernicterus develops. Kernicterus is a neurologic syndrome caused by deposition of bilirubin into central nervous system tissues. Kernicterus usually occurs several days after delivery and is characterized by loss of the Moro (ie, startle) reflex, posturing, poor feeding, inactivity, a bulging fontanelle, a high-pitched shrill cry, and seizures. Infants who survive kernicterus may go on to develop hypotonia, hearing loss, and mental retardation.

A very serious life-threatening condition observed in infants affected by Rh incompatibility is erythroblastosis fetalis, which is characterized by severe hemolytic anemia and jaundice. The most severe form of erythroblastosis fetalis is hydrops fetalis, which is characterized by high output cardiac failure, edema, ascites, pericardial effusion, and extramedullary hematopoiesis. Newborns with hydrops fetalis, a severe life-threatening hemolytic anemia, presents with at least two of the following: extremely pale with hematocrits usually less than 5, edema, pericardial effusions, pleural effusions and ascites. Hydrops fetalis often results in death of the infant shortly before or after delivery and requires an emergent exchange transfusion if there is to be any chance of infant survival. Hydrops fetalis is associated with a significant mortality rate estimated to be more than 50% ⁶⁹.

Rh incompatibility test

You, your partner and your baby can have tests to find out if you’re Rh-positive or negative and if your baby is at risk for Rh disease. You get a blood test at your first prenatal care visit to find out if you’re Rh-positive or Rh-negative. If you’re Rh-positive, there’s no risk of Rh disease in your baby. If you’re Rh-negative:

• You get a test called an antibody screen to see if you have Rh antibodies in your blood.
• If you don’t have Rh antibodies, your partner gets tested to see if he’s Rh-positive or negative.
• If your partner is Rh positive or you don’t know your partner’s Rh factor, your provider may recommend an amniocentesis to check your baby’s Rh factor or his bilirubin level. Bilirubin is a yellow substance that can build up in your baby’s blood when his liver isn’t working right. You get a second antibody test at 28 weeks of pregnancy. If this second test shows that your baby has anemia, your provider may do a Doppler ultrasound to check the flow of blood into your baby’s head.

The United States Preventive Services Task Force strongly recommends a Rh(D) blood type and antibody screen for all pregnant women at the initial prenatal visit ⁶⁸. Additionally, the United States Preventive Services Task Force recommends repeat antibody testing for all unsensitized Rh-negative mothers at 24 to 28 weeks of gestation, unless the father is Rh-negative. Antibody testing should also be performed at delivery. There are numerous outcomes after initial testing:

• If a mother is found to be Rh-positive, there is no risk of alloimmunization regardless of the Rh type of the fetus
• If the mother is Rh-negative, then alloimmunization can be assessed by an antibody screen
• If the Rh-negative mother is antibody positive, then a confirmatory study, such as a Coombs test, is needed to direct further management and monitoring of the pregnancy
• If the Rh-negative mother is antibody negative, paternal Rh testing can be performed as well.

If the father is also Rh-negative, then there is no risk for alloimmunization and complications of Rh incompatibility. On the other hand, a Rh-positive father gives the fetus a 50% risk of having Rh-positive erythrocytes and higher risk for the complications of Rh incompatibility. If the father is Rh-positive or the father’s Rh status cannot be determined, then more invasive testing may be needed.

For Rh-negative mothers that have potentially been exposed to fetal Rh-positive blood, one must assess fetomaternal hemorrhage. This assessment can be done with the rosette test for screening. Positive screens can be confirmed with the Kleihauer-Betke (KB) test or flow cytometry to determine the percentage of fetal blood cells (based on detecting fetal hemoglobin F) in the maternal circulation and the next steps in management ⁷⁰.

In a patient’s first affected pregnancy, surveillance of maternal antibody titers is recommended. Titers are repeated every month until 24 weeks of gestation and repeated more frequently in the third trimester. In a patient with a history of HDN, maternal titers are not utilized for determining the appropriate time to initiate fetal surveillance in a subsequent pregnancy. Fetal surveillance includes serial Middle Cerebral Artery dopplers every 1 to 2 weeks beginning at 24 weeks gestation and antenatal testing beginning at 32 weeks gestation. Middle Cerebral Artery peak systolic velocity of greater than 1.5 MoM is an indication for cordocentesis to determine fetal hematocrit and the need for intrauterine transfusion.

Rh incompatibility treatment

If your baby has Rh incompatibility, she can be treated to help prevent serious health problems.

If your baby has mild Rh incompatibility, you may be able to have a full-term pregnancy. Full term means your baby is born between 39 weeks and 40 weeks, 6 days. After birth, your baby may need certain medicine, and she may need treatment for jaundice. Sometimes Rh disease is so mild that your baby doesn’t need any treatment. Most babies recover fully from mild Rh incompatibility.

If your baby develops severe Rh incompatibility and severe anemia before birth, you may have to give birth early, before her due date. She may need a blood transfusion with new blood to replace red blood cells that the Rh antibodies destroyed. Babies can get a blood transfusion in the womb as early as 18 weeks of pregnancy; they also can get a transfusion after birth.

Emergent delivery of an infant with hydrops fetalis should be as nontraumatic as possible. Ideally, a neonatologist who is prepared to perform an exchange transfusion should attend to the infant immediately ⁷¹.

If your baby is born with severe jaundice, she needs quick treatment to prevent more serious complications.

If a mother has the potential to have Rh incompatibility during pregnancy, prophylactic Rh D immunoglobulin (RhoGAM®) should be administered to unsensitized Rh-negative women at 28 weeks gestation. If the neonate is found to be Rh-positive after delivery, those same unsensitized Rh-negative women should be given Rh D immunoglobulin (RhoGAM®) within 72 hours of delivery. The suggested Rh D immunoglobulin (RhoGAM®) dose in the United States is 300 mcg, which should be sufficient in covering up to 15 mL of Rh-positive erythrocytes (i.e., 30 mL of whole fetal blood) ⁶⁴. In addition, the American College of Obstetricians and Gynecologists recommends that all Rh-negative women giving birth to Rh-positive infants should initially undergo a qualitative screening test (rosette assay) and if indicated proceed with quantitative testing (KB test) to determine the correct number of doses of immune globulin required.

The same principle of Rh D immunoglobulin (RhoGAM®) immunoprophylaxis can be applied to Rh-negative mothers who have had high-risk events that could have potentially led to fetomaternal hemorrhage as previously discussed. The recommendations of American College of Obstetricians and Gynecologists for the dosing of Rh D immunoglobulin (RhoGAM®) vary depending on the scenario of potential fetomaternal hemorrhage. Smaller doses are considered for events that occur earlier in the pregnancy since the total fetal-placental blood volume is 3 mL (1.5 mL of fetal erythrocytes) at 12 weeks; therefore, at least 50 mcg should be considered for first-trimester events and 300 mcg if after 12 weeks ⁷².

Rhesus disease

Rhesus disease also called Rh incompatibility or Rh disease, is a dangerous kind of anemia. Anemia is when a person doesn’t have enough healthy red blood cells to carry oxygen to the rest of your body. Rhesus disease happens when your blood is Rh-negative and your baby’s blood is Rh-positive. This means your blood and your baby’s blood are incompatible (Rh incompatibility), so it’s not safe for them to mix together. If they do mix, your body makes Rh antibodies that may go from your body through the placenta into your baby’s body, where they attack and destroy her/his red blood cells. The placenta grows in your uterus (womb) and supplies your baby with food and oxygen through the umbilical cord.

Even though you and your baby don’t share blood, a small amount of your baby’s blood can mix with yours during pregnancy. This can happen if:

• Your baby’s blood crosses into your blood through the placenta.
• You have an amniocentesis (also called amnio) or chorionic villus sampling (also called CVS). These are prenatal tests that your health care provider may recommend during pregnancy.
• You have bleeding during pregnancy.
• Your baby’s in a breech position (feet-down instead of head-down) before labor and your provider tries to rotate (move) him around so he’s head-down.
• You get hit in the belly during pregnancy.
• You have a miscarriage or an ectopic pregnancy. A miscarriage is when a baby dies in the womb before 20 weeks of pregnancy. An ectopic pregnancy is when a fertilized egg implants itself outside of the uterus (womb) and begins to grow.

If you have Rh antibodies, you’re called Rh-sensitized.

Rh disease baby

Your baby is at risk for Rh disease only if you’re Rh-negative and your baby is Rh-positive. Your baby is Rh-positive depending on the blood of you and your baby’s father. Here’s how it works:

• If both you and your baby’s father are Rh-positive: Your baby’s blood is Rh-positive, and there’s no risk of Rh disease in your baby.
• If both you and your baby’s father are Rh-negative: Your baby’s blood is Rh-negative, and there’s no risk of Rh disease for your baby.
• If you’re Rh negative and your baby’s father is Rh-positive: Your baby’s blood may be Rh-positive. Your baby is at risk for Rh disease and needs to be checked closely.

Talk to your doctor about having your blood and your baby’s father’s blood tested to find out if your baby may be at risk.

If it’s your first pregnancy, your body usually doesn’t make enough Rh antibodies to harm your baby. But if you get pregnant again, your body produces more antibodies that can cause Rh disease in your baby.

Rh disease can cause serious problems for your baby, including:

• Anemia
• Brain damage
• Heart failure
• Jaundice. Jaundice can make your baby’s eyes and skin look yellow. A baby has jaundice when his liver isn’t fully developed or isn’t working. If jaundice is severe and isn’t treated, a baby can develop a kind of brain damage called kernicterus.
• Stillbirth. Stillbirth is when a baby dies in the womb after 20 weeks of pregnancy.
• Death after birth

If my baby has Rh disease, how is she treated?

If your baby has Rh disease, she can be treated to help prevent serious health problems.

If your baby has mild Rh disease, you may be able to have a full-term pregnancy. Full term means your baby is born between 39 weeks and 40 weeks, 6 days. After birth, your baby may need certain medicine, and she may need treatment for jaundice. Sometimes Rh disease is so mild that your baby doesn’t need any treatment. Most babies recover fully from mild Rh disease.

If your baby develops severe Rh disease and severe anemia before birth, you may have to give birth early, before her due date. She may need a blood transfusion with new blood to replace red blood cells that the Rh antibodies destroyed. Babies can get a blood transfusion in the womb as early as 18 weeks of pregnancy; they also can get a transfusion after birth.

If your baby is born with severe jaundice, she needs quick treatment to prevent more serious complications.

Rh disease causes

During pregnancy, red blood cells from the unborn baby can cross into the mother’s blood through the placenta.

If the mother is Rh-negative, her immune system treats Rh-positive fetal cells as if they were a foreign substance. The mother’s body makes antibodies against the fetal blood cells. These antibodies may cross back through the placenta into the developing baby. They destroy the baby’s circulating red blood cells.

When red blood cells are broken down, they make bilirubin. This causes an infant to become yellow (jaundiced). The level of bilirubin in the infant’s blood may range from mild to dangerously high.

Firstborn infants are often not affected unless the mother had past miscarriages or abortions. This would sensitize her immune system. This is because it takes time for the mother to develop antibodies. All children she has later who are also Rh-positive may be affected.

Rh incompatibility develops only when the mother is Rh-negative and the infant is Rh-positive. This problem has become less common in places that provide good prenatal care. This is because special Rho D immune globulin called RhoGAM are routinely used.

Rh disease prevention

Rh disease can be prevented in your baby if you get treatment at the right times. If you haven’t developed Rh antibodies, your doctor can give you a shot of Rh immunoglobulin called Rho D immune globulin (brand name RhoGAM®). RhoGAM can prevent your body from producing Rh antibodies so your baby and future pregnancies won’t get Rh disease. RhoGAM doesn’t work if your body has already started making Rh antibodies in a previous pregnancy. This is why it’s really important to get prenatal care as early as possible in every pregnancy.

If you’re RH-negative, you get Rho D immune globulin:

• At about 28 weeks of pregnancy
• Within 72 hours after the birth if your baby is Rh-positive or if his Rh is unknown
• After any situation in which your blood and your baby’s blood may mix, like amniocentesis or chorionic villus sampling, miscarriage, ectopic pregnancy or a hit to your belly.

Your provider watches your baby closely during pregnancy to check his health and for signs of anemia. In your third trimester, your provider may use amniocentesis or a special ultrasound called Doppler to check your baby. Ultrasound is a prenatal test that uses sound waves and a computer screen to show a picture of your baby inside the womb. A Doppler ultrasound helps a doctor check your baby’s heartbeat and measure the blood flow in the umbilical cord and certain blood vessels.

Rh disease symptoms

Rh incompatibility can cause symptoms ranging from very mild to deadly. In its mildest form, Rh incompatibility causes the destruction of red blood cells. There are no other effects.

After birth, the infant may have:

• Yellowing of the skin and whites of the eyes (jaundice)
• Low muscle tone (hypotonia) and lethargy

Before delivery, the mother may have more amniotic fluid around her unborn baby (polyhydramnios).

There may be:

• A positive direct Coombs test result
• Higher-than-normal levels of bilirubin in the baby’s umbilical cord blood
• Signs of red blood cell destruction in the infant’s blood

Rh disease possible complications

Rh disease complications may include:

• Brain damage due to high levels of bilirubin (kernicterus)
• Fluid buildup and swelling in the baby (hydrops fetalis)
• Problems with mental function, movement, hearing, speech, and seizures

Rh disease treatment

Rh disease or Rh incompatibility can be prevented with the use of RhoGAM. Therefore, prevention remains the best treatment. Treatment of an infant who is already affected depends on the severity of the condition.

Infants with mild Rh incompatibility may be treated with phototherapy using bilirubin lights. IV immune globulin may also be used. For infants severely affected, an exchange transfusion of blood may be needed. This is to decrease the levels of bilirubin in the blood.

Rh disease prognosis

Full recovery is expected for mild Rh disease or Rh incompatibility.

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