Amniocentesis

Contents

What is amniocentesis

What is amniocentesis

Amniocentesis (also called amnio) is a prenatal test that takes amniotic fluid from around your baby in the uterus (also called womb). The amniotic fluid is tested to see if your unborn baby has certain health conditions. A prenatal test is a medical test you get during pregnancy. Amniotic fluid contains cells that are normally shed from the unborn baby (fetus). Samples of these cells are obtained by withdrawing some amniotic fluid. Every cell in the amniotic fluid from the baby contains a complete set of the baby’s DNA. The chromosome analysis of these cells can be performed to determine abnormalities. In addition, the cells may be cultured and analyzed for enzymes, or for other materials that may indicate genetically transmitted diseases. Other studies can be done directly on the amniotic fluid including measurement of alpha-fetoprotein (AFP). Alpha-fetoprotein levels are often higher if your baby has a neural tube defect.

Amniocentesis test may be performed between 15 and 20 weeks of pregnancy to detect certain genetic diseases, chromosomal abnormalities such as Down syndrome, Edwards’ syndrome or Patau’s syndrome and neural tube defects. Amniocentesis test may also be performed at any point after 32 weeks of gestation to evaluate fetal lung maturity when there is an increased risk of or a need for premature delivery. Amniocentesis may also be done when it is suspected that a fetus has an infection or other illness or a blood type incompatibility with the mother and is therefore at risk of developing hemolytic disease.

Amniocentesis gives healthcare professionals direct information about how likely the baby will develop one or more conditions, which may be genetic (inherited) or develop during the pregnancy.

Doctors recommend you rest and avoid physical strain (such as lifting) after amniocentesis. If you experience any complications after the procedure, including abdominal cramping, leakage of fluid, vaginal bleeding, or signs of infection, call your doctor immediately.

The American College of Obstetricians and Gynecologists recommends that all pregnant women should be given the option of having amniocentesis performed. A health practitioner can help a pregnant woman weigh the pros and cons. Some women are at increased risk of birth defects due to their age or family/medical history while others may be advised against having the procedure if they have a history of premature labor, placental problems, or an incompetent cervix, for example. The procedure has some risks associated with it, such as a small chance of miscarriage, and provides information that can have a significant impact of the management of a pregnancy.

There is between a 0.25% and 0.50% risk of miscarriage and a very slight risk of uterine infection (less than .001%) after amniocentesis. In trained hands and under ultrasound guidance, the miscarriage rate may be even lower.

In most cases, your amniocentesis test results will be available within two weeks. Your doctor will explain the results to you and if a problem is diagnosed, give you information about ending the pregnancy or how best to care for your baby after birth.

Talk to your health care provider to see if amniocentesis is right for you.

Key points

Amniocentesis is a prenatal test that can diagnose certain birth defects and genetic conditions in your baby.
You may want to have an amniocentesis if you’re at increased risk of having a baby with a birth defect or genetic condition.
There’s a small risk of having a miscarriage after an amniocentesis. Miscarriage is when a baby dies in the womb before 20 weeks of pregnancy.
Having an amniocentesis is your choice. Talk with your partner and your provider to help you decide if an amniocentesis is right for you.
Amniocentesis can’t identify all genetic conditions and birth defects.

Amniocentesis test can diagnosis certain birth defects, including:

Down’s syndrome
Edwards’ syndrome and Patau’s syndrome – conditions that can result in miscarriage, stillbirth or (in babies that survive) severe physical problems and learning disabilities
Cystic fibrosis
Spina bifida
Genetic problems
Infection
Lung development

It is performed at 14 to 20 weeks.

It may be suggested for couples at higher risk for genetic disorders. It also provides DNA for paternity testing.

While still very much in use, recent advances in testing technology may eventually result in the decline in the use of amniocentesis. For example, there is a newer test called cell-free fetal DNA (cffDNA) that only requires a blood sample from the pregnant woman to screen for certain fetal chromosomal abnormalities, including Down syndrome, Edwards syndrome, and Patau syndrome (trisomy 13), and it can be performed as early as the 10th week of pregnancy. However, at this time, invasive diagnostic tests such as amniocentesis and chorionic villus sampling (CVS) are still needed to confirm the results.

When is amniocentesis done

When you are about 15 to 20 weeks pregnant, your doctor may offer amniocentesis. Amniocentesis is a prenatal test that detects or rules out certain genetic diseases, chromosomal abnormalities and open neural tube defects; after 32 weeks of pregnancy, amniocentesis can be used to evaluate fetal lung maturity; when it is suspected that a fetus has an infection or other illness; serially, about every 14 days, when it is suspected that a pregnant woman has an Rhesus (Rh) or other blood type incompatibility with her fetus. Amniocentesis also assesses lung maturity to see if the fetus can endure an early delivery. You can also find out the baby’s gender.

Doctors generally offer amniocentesis to women with an increased risk of having a baby with particular disorders, including those who:

Will be 35 or older when they deliver.
Have a close relative with a disorder.
Had a previous pregnancy or baby affected by a disorder.
Have test results (such as a high or low alpha-fetoprotein count) that may indicate an abnormality.

Doctors also offer amniocentesis to women with pregnancy complications, such as Rh-incompatibility, that necessitate early delivery. There are blood tests and ultrasound tests that can be done earlier in the pregnancy which may avoid the need for amniocentesis at times.

Figure 1. Amniocentesis

Figure 2. Normal placenta and pregnancy – the placenta attaches to the wall of the uterus (womb) and supplies the baby with food and oxygen through the umbilical cord.

Why is amniocentesis done?

The American College of Obstetricians and Gynecologists ¹ recommends that all pregnant women have the choice of having prenatal tests, like an amniocentesis.

Having an amniocentesis is your choice, even if you’re at risk of having a baby with a birth defect or genetic condition. Talk with your partner, provider and a genetic counselor about your testing options. A genetic counselor is a person who is trained to help you understand about genes, birth defects and other medical conditions that run in families, and how they can affect your health and your baby’s health. You also may want to talk to your religious and spiritual leaders to help you make decisions about testing for birth defects and genetic conditions during pregnancy.

Ask your provider about other prenatal tests and about seeing a provider like a maternal-fetal medicine specialist. This is an obstetrician with education and training to take care of women who have high-risk pregnancies. You can contact the Society for Maternal-Fetal Medicine (https://www.smfm.org/) to find a specialist in your area.

You may want to have an amniocentesis if your baby is at risk for certain conditions like:

Birth defects. These are health conditions that are present at birth. Birth defects change the shape or function of one or more parts of the body. They can cause problems in overall health, in how the body develops or in how the body works. Your provider can use amnio to diagnose certain birth defects, like birth defects of the brain and spine called neural tube defects. Examples of neural tube defects are spina bifida and anencephaly. Amnio doesn’t check for every birth defect. For example, it can’t check for certain heart problems or birth defects in a baby’s lip or mouth called cleft lip and palate. Some birth defects are genetic (caused by changes in genes).

Genetic and chromosomal conditions. These conditions are caused by changes in genes and chromosomes. A gene is part of your body’s cells that stores instructions for the way your body grows and works. Chromosomes are the structures in cells that hold genes. Genetic conditions include cystic fibrosis (also called CF), sickle cell disease and heart defects. A common chromosomal condition is Down syndrome. Sometimes these conditions are passed from parent to child, and sometimes they happen on their own.

If your baby’s at risk for having these conditions, you may have an amniocentesis at 15 to 20 weeks of pregnancy. It’s not recommended before 15 weeks because it has a higher risk of miscarriage and other complications. Miscarriage is when a baby dies in the womb before 20 weeks of pregnancy.

Later in pregnancy, you may have an amniocentesis to:

Check your baby’s lung development (also called fetal lung maturity). Your provider may recommend amniocentesis to check your baby’s amniotic fluid and find out if your baby’s lungs are developed for birth. This kind of amniocentesis is only done if you need to give birth early to help prevent pregnancy complications. It’s usually done between 32 and 39 weeks of pregnancy.
Check for infections or other health conditions in your baby. For example, if your baby’s at risk of Rh (Rhesus) incompatibility disease, your provider may use amniocentesis to check your baby for anemia. Rh (Rhesus) disease a dangerous kind of anemia that’s preventable if it’s treated during pregnancy. Anemia is when a person doesn’t have enough healthy red blood cells to carry oxygen to the rest of the body.
Treat polyhydramnios (therapeutic amniocentesis). Polyhydramnios is when you have too much amniotic fluid. Amniotic fluid is the fluid that surrounds your baby in the womb. Polyhydramnios may increase your risk of having pregnancy complications, like premature birth (birth before 37 weeks of pregnancy). Your provider can use amnio to drain extra fluid from the womb.

Are you at risk of having a baby with a birth defect or a genetic or chromosomal condition?

You may be at increased risk of having a baby with one of these conditions if:

You’re 35 or older. The risk of having a baby with a chromosomal condition, like Down syndrome, increases as you get older.
You have a child with a birth defect or you had a previous pregnancy with a birth defect. Having a birth defect in a previous pregnancy makes you more likely to have a birth defect in another pregnancy.
You have a family history of a genetic condition. If you, your partner or a member of either of your families has a genetic condition, like cystic fibrosis (CF), fragile X syndrome, sickle cell disease, Tay-Sachs or thalassemia, you may want to have an amniocentesis to find out if your baby also has the condition. You can get carrier screening for genetic conditions before or during early pregnancy. Carrier screening test checks your blood or saliva to see if you’re a carrier of certain genetic conditions that could affect your baby. If you’re a carrier, you don’t have the condition yourself, but you have a gene change for it that you can pass to your baby. If both you and your partner are carriers of the same condition, the risk that your baby has the condition increases.
Your prenatal screening tests results are abnormal. There are no risks to you or your baby when you have a screening test, but it doesn’t tell you for sure if your baby has a health condition. A diagnostic test, like amniocentesis, can diagnose a condition. If you have abnormal results from a screening test, like first-trimester screening or cell-free DNA testing, you may want to have a diagnostic test, like amniocentesis.

When is amniocentesis ordered?

While amniocentesis is safe and has been performed for many years, it is an invasive procedure that poses a slight risk of injury to the fetus and of miscarriage. For this reason, it is not performed routinely with each pregnancy.

Genetic amniotic fluid analysis may be offered as part of second trimester prenatal testing and is performed primarily between 15 and 20 weeks gestation if:

A woman is 35 years of age or older
A woman has an abnormality on a first trimester Down syndrome screen or second trimester maternal serum screen, such as an increased or decreased alpha-feto protein (AFP) level
A woman had a previous child or pregnancy with a chromosomal abnormality or birth defect
There is a strong family history of a specific genetic disorder
A parent has an inherited disorder or both parents have a gene for an inherited disorder
An abnormality has been detected on a fetal ultrasound

Fetal lung maturity amniotic fluid testing is ordered when there is a risk of premature delivery, at any time after 32 weeks gestation.

Biochemical testing is sometimes ordered to monitor bilirubin levels when a woman has been sensitized or it is suspected that she has become sensitized (has developed antibodies) to red blood cell antigens and there may be an Rh or other blood type incompatibility with the fetus. In this case, serial testing for bilirubin may be performed, usually about every 14 days.

An amniotic fluid analysis may be performed in late pregnancy to check for fetal distress and to diagnose a fetal infection.

Genetic amniocentesis

Genetic amniocentesis can provide information about your baby’s genetic makeup. Generally, genetic amniocentesis is offered when the test results might have a significant impact on the management of the pregnancy or your desire to continue the pregnancy.

Genetic amniocentesis is usually done between week 15 and 20 of pregnancy. Amniocentesis done before week 15 of pregnancy has been associated with a higher rate of complications.

You might consider genetic amniocentesis if:

You had positive results from a prenatal screening test. If the results of a screening test — such as the first trimester screen or prenatal cell-free DNA screening — are positive or worrisome, you might opt for amniocentesis to confirm or rule out a diagnosis.
You had a chromosomal condition or a neural tube defect in a previous pregnancy. If a previous pregnancy was affected by conditions such as Down syndrome or a neural tube defect — a serious condition affecting the brain or spinal cord — your health care provider might suggest amniocentesis to confirm or rule out these disorders.
You’re 35 or older. Babies born to women 35 and older have a higher risk of chromosomal conditions, such as Down syndrome. Your health care provider might suggest amniocentesis to rule out these conditions.
You have a family history of a specific genetic condition, or you or your partner is a known carrier of a genetic condition. In addition to identifying Down syndrome and spina bifida, amniocentesis can be used to diagnose many other conditions — such as cystic fibrosis.
You have abnormal ultrasound findings. Your health care provider might recommend amniocentesis to diagnose or rule out genetic conditions associated with abnormal ultrasound findings.

Remember, genetic amniocentesis is typically offered when the test results might have a significant impact on management of the pregnancy. Ultimately, the decision to have genetic amniocentesis is up to you. Your health care provider or genetic counselor can help you weigh all the factors in the decision.

Fetal lung maturity amniocentesis

Fetal lung maturity amniocentesis can determine whether a baby’s lungs are ready for birth. This type of amniocentesis is done only if early delivery — either through induction or C-section — is being considered to prevent pregnancy complications for the mother in a non-emergency situation. It’s usually done between 32 and 39 weeks of pregnancy. Earlier than 32 weeks, a baby’s lungs are unlikely to be fully developed.

Amniocentesis isn’t appropriate for everyone, however. Your health care provider might discourage amniocentesis if you have an infection, such as HIV/AIDS, hepatitis B or hepatitis C. These infections can be transferred to your baby during amniocentesis.

Amniocentesis procedure

Amniocentesis test preparation

You may be instructed to have either a full or empty bladder prior to amniocentesis, depending on when during your pregnancy the testing is being performed; follow any instructions you are given.

If you’re having amniocentesis done before week 20 of pregnancy, it might be helpful to have your bladder full during the procedure to support the uterus. Drink plenty of fluids before your appointment. After 20 weeks of pregnancy, your bladder should be empty during amniocentesis to minimize the chance of puncture.

During the amniocentesis procedure

Here’s what happens when you have an amniocentesis:

You lie on your back on an exam table and expose your abdomen. Your health care provider will apply a special gel to your abdomen and then use a small device known as an ultrasound transducer to show your baby’s position on a monitor.
Your health care provider will use ultrasound to determine the baby’s exact location in your uterus.
Your provider moves an ultrasound wand (also called transducer) across your belly to find your baby and the placenta. The placenta grows in your uterus and supplies your baby with food and oxygen through the umbilical cord. Ultrasound uses sound waves and a computer screen to show a picture of your baby inside the womb.
Your provider cleans your belly with an antibacterial liquid that kills germs on your skin.
Using ultrasound as a guide, your provider puts a thin needle through your belly and uterus into the amniotic sac. The amniotic sac (also called bag of waters) is the sac (bag) inside the uterus that holds your growing baby. It’s filled with amniotic fluid.
Using the ultrasound for guidance, your doctor carefully inserts a long, but thin, hollow needle through your abdomen and into the amniotic sac. Your doctor then extracts about four teaspoons (less than 1 ounce) of amniotic fluid. The amniotic fluid contains fetal cells from your baby. Once the amniotic fluid sample is taken, your provider uses the ultrasound to check that your baby’s heartbeat is healthy.
You should receive Rh (Rhesus) immune globulin (RhIG) at the time of amniocentesis if you are an Rh-negative unsensitized patient.

Your provider sends the amniotic fluid sample to a lab where your baby’s cells are separated from the amniotic fluid. The cells grow for about 10 to 12 days at the lab and then they’re tested for birth defects and genetic conditions. The lab also can test the amniotic fluid for proteins like alpha-fetoprotein (also called AFP). Test results usually are available within 2 to 3 weeks.

If amniocentesis shows that your baby has a health condition, talk to your provider about your options. For example, your baby may be able to be treated with medicines or surgery before or after birth. Knowing about a birth defect before birth may help you get ready to care for your baby. And you can make plans for your baby’s birth with your provider to make sure your baby gets special care or treatment he may need right after he’s born.

After the amniocentesis procedure

After the amniocentesis, your health care provider will continue using the ultrasound to monitor your baby’s heart rate. You might experience cramping or mild pelvic discomfort after an amniocentesis.

You can resume your normal activity level after the procedure. However, you might consider avoiding strenuous exercise and sexual activity for a day or two.

Meanwhile, the sample of amniotic fluid will be analyzed in a lab. Some results might be available within a few days. Other results might take up to four weeks.

Contact your health care provider if you have:

Loss of vaginal fluid or vaginal bleeding
Severe uterine cramping that lasts more than a few hours
Fever
Redness and inflammation where the needle was inserted
Unusual fetal activity or a lack of fetal movement

Does amniocentesis hurt?

Amniocentesis is done in an examination room, either with or without local anesthesia. It typically takes just a few minutes, during which you must lie very still. Most women have only mild discomfort during an amniocentesis. You may have a stinging feeling when the needle enters your skin, feel cramping when the needle enters the uterus or feel pressure when the fluid is removed. After the test, your provider may tell you to take it easy for the rest of the day and not to exercise or have sex for a day or two.

What does amniocentesis test for?

Amniotic fluid surrounds, protects, and nourishes a growing fetus during pregnancy. Amniotic fluid analysis involves a variety of tests that can be performed to evaluate the health of a fetus.

Amniotic fluid allows a fetus to move relatively freely within the uterus, keeps the umbilical cord from being compressed, and helps maintain a stable temperature. Contained within the amniotic sac, amniotic fluid is normally a clear to pale yellow liquid that contains proteins, nutrients, hormones, and antibodies.

Amniotic fluid begins forming one to two weeks after conception and increases in volume until there is about a quart at 36 weeks of pregnancy. The fluid is absorbed and continually renewed.

The fetus swallows and inhales amniotic fluid and releases urine into it. Cells from various parts of the fetus’s body and chemicals produced by the fetus are present in the amniotic fluid. This allows the fluid to be sampled and tested to evaluate fetal health.

Amniotic fluid contains skin cells shed from the baby that can be used to diagnose chromosomal problems, such as Down syndrome.

Amniotic fluid also contains alpha-fetoprotein (AFP), a substance produced by the baby. Levels of alpha-fetoprotein may also indicate whether a baby has problems affecting the spine or other areas of the body.

Amniocentesis helps in detecting or ruling out Down’s syndrome, which causes intellectual disabilty, congenital heart defects, and physical characteristics such as skin folds near the eyes. Amniocentesis also detects neural tube defects such as spina bifida. Babies born with spina bifida have a backbone that did not close properly. Serious complications of spina bifida can include leg paralysis, bladder and kidney defects, brain swelling (hydrocephalus), and intellectual disability.

If your pregnancy is complicated by a condition such as Rh-incombatibility, your doctor can use amniocentesis to find out if your baby’s lungs are developed enough to endure an early delivery. Many more diagnoses are available through amniocentesis.

For genetic testing and chromosome analysis, fetal cells in the amniotic fluid are cultured and grown for 10-12 days in the laboratory, then are analyzed. Biochemical tests, such as bilirubin and alpha-fetoprotein (AFP), and sometimes genetic tests can be performed directly on the amniotic fluid.

Chromosomal conditions

Chromosomal conditions are conditions that affect the chromosomes (parts of the body’s cells that carry genes). For example:

Down syndrome – a condition that affects a person’s physical appearance, mental development and learning ability; it is the result of an extra chromosome, known as trisomy-21
Edwards syndrome – a condition that causes severe physical and mental abnormalities; it is the result of an extra chromosome, known as trisomy-18
Patow syndrome – a rare but serious condition where babies rarely survive for more than a few days; it is the result of an extra chromosome, known as trisomy-13.

Blood disorders

Amniocentesis can also be used to check for inherited blood disorders, such as:

Sickle cell anemia – a condition where red blood cells (which carry oxygen around the body) are an unusual shape and texture
Thalassemia – a condition that affects the body’s ability to create red blood cells
Hemophilia – a condition that affects the blood’s ability to clot.

Neural tube defects

Amniocentesis can test for neural tube defects. The neural tube is a primitive tissue structure inside which the embryo (fertilized egg) grows during its first month of life. As the embryo develops, the neural tube changes and eventually forms the spine and nervous system.

A neural tube defect can lead to conditions such as spina bifida, which can cause learning difficulties and paralysis (weakness) of the lower limbs.

Musculoskeletal disorders

Amniocentesis can also be used to diagnose conditions that affect the musculoskeletal system (your bones and muscles), such as muscular dystrophy. Muscular dystrophy is an inherited condition that causes muscles to gradually weaken, resulting in an increasing level of disability.
Other genetic conditions

As well as helping diagnose chromosomal conditions, blood disorders, neural tube defects and musculoskeletal disorders, amniocentesis can also help diagnose a number of genetic conditions, such as Marfan syndrome. This condition affects the tissues that provide support.

Amniocentesis accuracy

Amniocentesis is estimated to give a definitive result in 98-99% of cases.

However, amniocentesis can’t test for every birth defect and, in a small number of cases, it’s not possible to get a conclusive result.

For many women who have amniocentesis, the results of the procedure will be “normal”. This means that none of the conditions that were tested for were found in the baby.

However, a normal result doesn’t guarantee that your baby will be completely healthy as the test only checks for conditions caused by faulty genes, and it can’t exclude every condition.

An amniocentesis is an accurate way of testing for most chromosome problems. However mosaicism (when some, but not all of the baby’s cells have a chromosomal abnormality) and very small chromosome abnormalities cannot be excluded.
Amniocentesis cannot detect all problems with a baby. Having an amniocentesis does not guarantee that your baby will not have a birth defect as most are not caused by abnormalities of the chromosomes.

If your test is “positive”, your baby has one of the conditions they were tested for. In this instance, the implications will be fully discussed with you and you’ll need to decide how to proceed.

What does the amniocentesis test result mean?

Genetic tests, chromosome analysis and testing for birth defects

Women should discuss their test results with their health practitioner and with a genetic counselor.

If a chromosomal abnormality or a genetic disorder is detected, then the baby likely will have the associated condition. However, test results may not predict the condition’s severity or prognosis.

Normal results make it less likely that a fetus has an inherited condition, but all genetic conditions cannot be ruled out. Not every genetic disorder or chromosomal abnormality will be detected with this testing.

If an increased or decreased alpha fetoprotein suggests a structural abnormality, such as an open neural tube defect, then additional testing and imaging may be performed to determine the severity of the condition and the best course of action.

If amniocentesis indicates that your baby has a chromosomal or genetic condition that can’t be treated, you might face wrenching decisions — such as whether to continue the pregnancy. Seek support from your health care team and your loved ones during this difficult time.

Fetal lung maturity

If testing indicates that there are low levels of surfactants, then a fetus’s lungs have not yet matured and measures can be taken to attempt to delay delivery, to promote lung maturity, and – when necessary – to treat the baby as soon as it is born. If the levels of surfactants are deemed high enough, then the baby may be safely delivered without increased risk of complications from lung immaturity.

Rh or other blood type incompatibility

Increasing bilirubin concentrations in a fetus with a fetal-maternal blood type incompatibility indicate increasing destruction of red blood cells (RBCs) and the likelihood that the fetus will be born with hemolytic disease of the newborn, requiring treatment depending on the severity.

Fetal distress or infection

Evaluation of amniotic fluid color:

Green-tinged indicates that meconium, the fetus’s first stool, has been released.
Yellow to amber may indicate bilirubin in the fluid.
Red-tinged indicates blood from the mother or the fetus.

Cultures of the amniotic fluid will indicate whether or not an infection is present.

What happens if a condition is found?

If the test finds that your baby will be born with a condition, you can speak to a number of specialists about what this means.

These could include your midwife, a consultant pediatrician, a geneticist and/or a genetic counselor.

They’ll be able to give you detailed information about the condition – including the possible symptoms your child may have, the treatment and support they might need, and whether their life expectancy will be affected – to help you decide what to do.

A baby born with one of these conditions will always have the condition, so you’ll need to consider your options carefully. Your main options are:

continue with your pregnancy while gathering information about the condition, so you’re prepared for caring for your baby
have a termination (abortion) – read more about termination for fetal abnormalities

This can be a very difficult decision, but you don’t have to make it on your own.

As well as discussing it with specialist healthcare professionals, talk things over with your partner and speak to close friends and family, if you think it might help.

Is there anything else I should know about amniocentesis test results?

Both blood contamination and stool from the baby (meconium) in the amniotic fluid can affect some chemical test results.

An alternative to amniotic fluid analysis for chromosomal analysis and genetic testing is chorionic villus sampling (CVS), which can be performed earlier, between 10 and 13 weeks of pregnancy. This first trimester procedure collects a placenta tissue sample at the site of implantation and carries about the same risks as amniocentesis. Chorionic villus sampling (CVS) cannot, however, detect neural tube defects.

Performed on a blood sample obtained from the mother, the first trimester screen for Down syndrome and the second trimester screen for Down syndrome and open neural tube defects assess the risk of a fetus having these conditions but are not diagnostic. In most cases, the subsequent amniotic fluid analysis will be normal; only a small percentage of those with an abnormal blood screening test result will actually have an affected baby.

Amniocentesis risks and complications

Serious complications from amniocentesis are rare.

Some women may have other complications from amniocentesis, including:

Miscarriage. Less than 1 in 200 women (less than 1 percent) have a miscarriage after an amniocentesis. Research suggests that the risk of pregnancy loss is higher for amniocentesis done before 15 weeks of pregnancy. Second-trimester amniocentesis carries a slight risk of miscarriage — about 0.6 percent.
Infection in the uterus. Very rarely, amniocentesis might trigger a uterine infection.
Cramping, spotting or leaking amniotic fluid. About 1 to 2 in 100 women (1 to 2 percent) have these problems.
Passing infection to your baby. If you have an infection, like HIV/AIDS, hepatitis C, or toxomplasmosis, you may pass it to your baby during amniocentesis. HIV is the virus that causes AIDS. Toxoplasmosis is an infection you can get from eating undercooked meat or touching cat poop.
Rhesus (RhD) sensitization. Rarely, amniocentesis might cause a small amount of your baby’s blood to mix with your blood. If you’re Rh-negative and your baby is Rh-positive and you haven’t developed antibodies to Rh positive blood, you may get a shot called Rh immune globulin (RhIG) after amniocentesis to help protect your baby. This will prevent your body from producing Rh antibodies that can cross the placenta and damage the baby’s red blood cells. A blood test can detect if you’ve begun to produce antibodies.
Leaking amniotic fluid. Rarely, amniotic fluid leaks through the vagina after amniocentesis. However, in most cases the amount of fluid lost is small and stops within one week, and the pregnancy is likely to proceed normally.
Needle injury. During amniocentesis the baby might move an arm or leg into the path of the needle. Serious needle injuries are rare.
Club foot. Club foot, also known as talipes, is a congenital (present at birth) deformity of the ankle and foot. Having amniocentesis early (before week 15 of the pregnancy) has been associated with an increased risk of the unborn baby developing club foot. Because of the increased risk of a baby developing club foot, amniocentesis isn’t recommended before 15 weeks of pregnancy.

If you have any of these signs or symptoms after an amniocentesis, call your healthcare provider immediately:

Feeling a change in your baby’s movement
Bleeding or leaking fluid from your vagina
Fever
Redness and swelling where your provider inserted the needle
Strong belly cramps that last more than a few hours.

Rh (Rhesus) factor

The Rh (Rhesus) blood group was named after the rhesus monkey in which it was first studied. In humans, this group includes several Rh antigens (factors). The most prevalent of these is antigen D, a transmembrane protein.

If the Rh antigens are present on the red blood cell membranes, the blood is said to be Rh-positive. Conversely, if the red blood cells do not have Rh antigens, the blood is called Rh-negative. The presence (or absence) of Rh antigens is an inherited trait. Anti-Rh antibodies (anti-Rh) form only in Rh-negative individuals in response to the presence of red blood cells with Rh antigens. This happens, for example, if an individual with Rh-negative blood receives a transfusion of Rh-positive blood. The Rh antigens stimulate the recipient to begin producing anti-Rh antibodies. Generally, this initial transfusion has no serious consequences, but if an individual with Rh-negative blood—who is now sensitized to Rh-positive blood—receives another transfusion of Rh-positive blood some months later, the donated red cells are likely to agglutinate.

A similar situation of Rh incompatibility arises when an Rh-negative woman is pregnant with an Rh-positive fetus. Her first pregnancy with an Rh-positive fetus would probably be uneventful. However, if at the time of the infant’s birth (or if a miscarriage occurs) the placental membranes that separated the maternal blood from the fetal blood during the pregnancy tear, some of the infant’s Rh-positive blood cells may enter the maternal circulation. These Rh-positive cells may then stimulate the maternal tissues to produce anti-Rh antibodies. If a woman who has already developed anti-Rh antibodies becomes pregnant with a second Rh-positive fetus, these antibodies, called hemolysins, cross the placental membrane and destroy the fetal red blood cells. The fetus then develops a condition called erythroblastosis fetalis, or hemolytic disease of the fetus and newborn.

Erythroblastosis fetalis is extremely rare today because obstetricians carefully track Rh status. An Rh-negative woman who might carry an Rh-positive fetus is given an injection of a drug called RhoGAM at week 28 of her pregnancy and after delivery of an Rh-positive baby. Rhogam is a preparation of anti-Rh antibodies, which bind to and shield any Rh-positive fetal cells that might contact the woman’s cells and sensitize her immune system. RhoGAM must be given within 72 hours of possible contact with Rh-positive cells—including giving birth, terminating a pregnancy, miscarrying, or undergoing amniocentesis (a prenatal test in which a needle is inserted into the uterus).

Amniocentesis vs CVS

CVS (chorionic villus sampling) is a prenatal test carried out during pregnancy to detect specific abnormalities in an unborn baby. During CVS (chorionic villus sampling) a sample of cells is taken from the placenta (the organ that links the mother’s blood supply with her unborn baby’s) and tested for genetic abnormalities. CVS (chorionic villus sampling) is a test you may be offered during pregnancy to check if your baby has a genetic or chromosomal condition, such as Down’s, Edwards’ or Patau’s syndromes.

CVS is different from another prenatal test called amniocentesis. Amniocentesis is performed a little later in pregnancy at around 15 to 20 weeks.

You can get CVS early in pregnancy, between 10 and 13 weeks.

Chorionic villus sampling (CVS) cannot, however, detect neural tube defects. These are birth defects affecting the brain and the spinal cord, such as spina bifida, which can usually be detected with an ultrasound scan.
Amniocentesis can test for neural tube defects.

CVS isn’t routinely offered to all pregnant women because there’s a small chance of miscarriage after the test. CVS is only offered if there’s a high risk your baby could have a genetic or chromosomal condition.

It’s important to remember that you don’t have to have CVS if it’s offered. It’s up to you to decide whether you want it.

A CVS test done at 10 to 13 weeks to diagnose certain birth defects, including:

Chromosomal disorders, including:
- Down’s syndrome – a condition that typically causes some level of learning disability and a characteristic range of physical features
- Edwards’ syndrome and Patau’s syndrome – conditions that can result in miscarriage, stillbirth or (in babies that survive) severe physical problems and learning disabilities
Genetic disorders, such as:
- Cystic fibrosis – a condition in which the lungs and digestive system become clogged with thick, sticky mucus
- Duchenne muscular dystrophy – a condition that causes progressive muscle weakness and disability
- Thalassaemia – a condition that affects the red blood cells, which can cause anemia, restricted growth and organ damage
- Sickle-cell disease – where the red blood cells develop abnormally and are unable to carry oxygen around the body properly
- Phenylketonuria (PKU) – where your body cannot break down a substance called phenylalanine, which can build up to dangerous levels in the brain

CVS may be suggested for couples at higher risk for genetic disorders.

This could be because:

an earlier antenatal screening test has suggested there may be a problem, such as Down’s syndrome, Edwards’ syndrome or Patau’s syndrome
you’ve had a previous pregnancy with these problems
you have a family history of a genetic condition, such as sickle cell disease, thalassaemia, cystic fibrosis or muscular dystrophy, and an abnormality is detected in your baby during a routine ultrasound scan

CVS also provides DNA for paternity testing.

Talk to your doctor about having CVS, amniocentesis or other prenatal tests.

Deciding whether to have CVS

If you’re offered CVS, ask your doctor or midwife what the procedure involves and what the risks and benefits are before deciding whether to have it.

You may also find it helpful to contact a support group, such as Antenatal Results and Choices (https://www.arc-uk.org/). Antenatal Results and Choices is a charity that offers information, advice and support on all issues related to screening during pregnancy.

What are some reasons for having CVS?

The test will usually tell you whether your baby will be born with any of the conditions that were tested for.

Your provider should discuss prenatal testing with you and may offer you CVS. And you can ask to have CVS. You may want to have CVS if you’re at risk for having a baby with a genetic abnormality. These risks include:

Being 35 or older: The risk of having a baby with certain birth defects or genetic abnormalities, such as Down syndrome, increases as you get older.
Having a previous child or pregnancy with a birth defect: If you had a child or a pregnancy with a birth defect in the past, your provider should offer you testing.
Abnormal screening test results: If you had abnormal results from a pregnancy screening test, your provider should discuss CVS with you. CVS can provide specific information to confirm if there is an abnormality in the baby. Most babies with abnormal screening test results don’t have problems and are born healthy.
Family history of a genetic health problem: If you or your partner has a certain genetic disease (a health condition that gets passed down to a baby from mom or dad), or a close family member with a disease, such as cystic fibrosis or sickle cell anemia, you may want to have CVS.

If no problem is found, it may be reassuring. A result showing that a condition was detected will give you plenty of time to decide how you want to proceed with your pregnancy.

Reasons not to have CVS

There is a 0.5-1% chance you could have a miscarriage after the procedure. You may feel this risk outweighs the potential benefits of the test.

Some women decide they don’t want to know if there’s a problem with their baby until later on. You may choose to have an alternative test called amniocentesis later in your pregnancy instead, or you might just want to find out when your baby is born.

What are CVS risks or side effects?

CVS does involve a small risk of miscarriage. The American College of Obstetricians and Gynecologists reports that 1 in 100 (1 percent) women has a miscarriage following testing.

However, it’s difficult to determine which miscarriages would have happened anyway, and which are the result of the CVS procedure. Some recent research has suggested that only a very small number of miscarriages that occur after CVS are a direct result of the procedure.

Most miscarriages that happened after CVS occur within three days of the procedure. However, in some cases a miscarriage can occur later than this (up to two weeks afterwards). There’s no evidence to suggest you can do anything during this time to reduce your risk.

The risk of miscarriage after CVS is considered to be similar to that of an alternative test called amniocentesis, which is carried out slightly later in pregnancy.

Inadequate sample

In around 1% of procedures, the sample of cells removed may not be suitable for testing. This could be because not enough cells were taken, or because the sample was contaminated with cells from the mother.

If the sample is unsuitable, it may be necessary for the CVS procedure to be carried out again, or to wait a few weeks to have amniocentesis instead.

Infection

As with all types of surgical procedures, there’s a risk of infection during or after CVS.

However, severe infection occurs in less than 1 in every 1,000 procedures.

Rhesus sensitization

If your blood type is rhesus (RhD) negative, but your baby’s blood type is RhD positive, it’s possible for sensitization to occur during CVS.

This is where some of your baby’s blood enters your bloodstream and your body starts to produce antibodies to attack it. If it’s not treated, this can cause the baby to develop rhesus disease.

If you don’t already know your blood type, a blood test will be carried out before CVS to see if there’s a risk of sensitization. An injection of a medication called anti-D immunoglobulin can be given to stop sensitization occurring, if necessary.

What if you’re not sure about having CVS?

Choosing to have CVS is a personal decision. Talking with genetic counselors and your health care provider may help you make decisions about testing for birth defects during pregnancy.

Ask your doctor about other prenatal test options and how you can find a doctor who is trained and experienced in offering specific tests. Learn as much as you can about any prenatal tests your provider recommends to make the right decisions for you and your baby.

What are the alternatives to CVS?

An alternative to CVS is a test called amniocentesis. This is where a small sample of amniotic fluid (the fluid that surrounds the baby in the womb) is removed for testing.

Amniocentesis usually carried out between the 15th and 20th week of pregnancy, although it can be performed later than this if necessary.

Amniocentesis test has a similar risk of causing a miscarriage, but your pregnancy will be at a more advanced stage before you can get the results, so you’ll have a bit less time to consider your options.

If you’re offered tests to look for a genetic or chromosomal condition in your baby, a specialist involved in carrying out the test will be able to discuss the different options with you, and help you make a decision.

Figure 3. Amniocentesis vs CVS

How is the CVS test done?

The CVS test itself takes about 10 minutes, although the whole consultation may take about 30 to 45 minutes.

A health care provider with expertise in performing CVS takes a tiny piece of tissue from the placenta, which has cells from your unborn baby, to check for problems. The placenta grows with your baby in your uterus (womb). It gives your baby food and oxygen through the umbilical cord.

There are two kinds of CVS:

Testing through the belly (called transabdominal CVS) — Your provider puts a thin needle through your belly into the womb. She then uses the needle to take a small sample of the placenta tissue.
Testing through the cervix (called transcervical CVS) — Your provider places a thin tube through your vagina and cervix (the opening to the uterus that sits at the top of the vagina). The tube gently sucks in a tiny sample of the placenta tissue (see Figure 3 above).

Your healthcare provider sends the tissue sample to a lab where it is examined and tested. Test results are usually ready in about 7 days.

Some women find that CVS is painless. Others feel cramping, similar to period cramps, when the sample is taken. Some women who have testing through the cervix say it feels like having a Pap smear.

After CVS, relax for the rest of the day. You may have spotting or cramping for a few hours after the test. Call your health care provider right away if you have heavy bleeding, fever or contractions.

CVS Test Results

After chorionic villus sampling (CVS) has been carried out, the sample of cells will be sent to a laboratory to be tested.

The number of chromosomes (bundles of genes) in the cells can be counted, and the structure of the chromosomes can be checked for any abnormalities.

If CVS is being carried out to test for a specific genetic disorder, the cells in the sample can also be tested for this.

Getting the results

The first results should be available within three working days, and this will tell you whether a chromosomal condition such as Down’s syndrome, Edwards’ syndrome or Patau’s syndrome has been found.

If rarer conditions are also being tested for, it can take two to three weeks or more for the results to come back.

You can usually choose whether to get the results over the phone or during a face-to-face meeting at the hospital or at home. You’ll also receive written confirmation of the results.

How reliable are the CVS test results?

CVS is estimated to give a definitive result in around 99% of cases. However, it cannot test for every birth defect and it’s not always possible to get a conclusive result.

In a very small number of cases, the results of CVS cannot establish with certainty that the chromosomes in the baby are normal or not. This might be because the sample of cells removed was too small or there’s a possibility the abnormality is just in the placenta and not the baby.

If this happens, it may be necessary to have amniocentesis (an alternative test, in which a sample of amniotic fluid is taken from the mother) a few weeks later to confirm a diagnosis.

What the CVS test results mean

For many women who have CVS, the results of the procedure will be “normal”. This means that none of the conditions that were tested for were found in the baby.

However, a normal result doesn’t guarantee that your baby will be completely healthy, as the test only checks for conditions caused by faulty genes, and it cannot exclude every possible condition.

What happens if a condition is found

If the test shows that your baby does have a birth defect, you can speak to a number of specialists about what this means. These could include your midwife, a consultant pediatrician, a geneticist and/or a genetic counselor.