What is chorionic villus sampling

Chorionic villus sampling (CVS) is a prenatal test carried out during pregnancy to detect specific birth defects and genetic abnormalities in an unborn baby. 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 defects. Genetic abnormalities are changes in the genes that are passed down to a baby from mom or dad. These genetic changes can cause health problems for a baby.

You can get chorionic villus sampling early in pregnancy, between 10 and 13 weeks. In special circumstances, the chorionic villus sampling might be carried out later, but it should not be done before 10 weeks of pregnancy. Chorionic villus sampling isn’t given to all pregnant women because there’s a small chance of miscarriage after the test.

The risk of chorionic villus sampling causing complications, such as miscarriage or birth defects in the baby, would be higher if it were carried out before week 10 of the pregnancy.

Chorionic villus sampling is offered in pregnancies where there is a high risk of the baby having a serious inherited condition. You may want to have chorionic villus sampling if you’re at risk for having a baby with a genetic abnormality. These risks include:

• You are over 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.
• You have had a previous pregnancy where the baby had problems such as a chromosome abnormality or another serious health condition. If you had a child or a pregnancy with a birth defect in the past, your provider should offer you testing.
• You have a 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, muscular dystrophy, thalassemia or sickle cell anemia, you may want to have chorionic villus sampling.
• An antenatal screening test, such as the combined first trimester screening test or the non-invasive prenatal test, has suggested that the baby may have a health problem e.g., Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. If you had abnormal results from a pregnancy screening test, your provider should discuss chorionic villus sampling with you. Chorionic villus sampling 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.

Chorionic villus sampling is different from another prenatal test called amniocentesis (also called amnio). Amniocentesis is performed a little later in pregnancy. Talk to your doctor about having chorionic villus sampling, amniocentesis or other prenatal tests.

How does chorionic villus sampling work?

Early in pregnancy, the embryo divides into two parts. One part develops into the baby; the other part develops into the placenta.

The part of the embryo that forms the placenta starts out as finger-like sections known as ‘chorionic villi’. These burrow into the wall of the womb to get close to the mother’s blood vessels.

The chorionic villi are formed when the fertilised egg divides, which means they have exactly the same DNA as the embryo, including any possible genetic abnormality. Any defect in the chorionic villi will also be present in the fetus.

What conditions can chorionic villus sampling detect?

Chorionic villus sampling test can help detect hundreds of genetic disorders. Abnormal results may be due to many different genetic conditions, 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
• Cystic fibrosis – a condition where the lungs and digestive system become clogged with thick, sticky mucus
• Duchenne muscular dystrophy – a condition that causes progressive muscle weakness and disability
• Tay-Sachs disease
• Thalassemia – a condition that affects the red blood cells, which can cause anaemia, 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 – where your body can’t break down a substance called phenylalanine, which can build up to dangerous levels in the brain

Chorionic villus sampling can’t 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.

What if I’m not sure about having chorionic villus sampling?

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

Choosing to have chorionic villus sampling is a personal decision. Talking with genetic counselors, your health care provider, and religious and spiritual leaders can help you make decisions about testing for birth defects during pregnancy.

Ask your provider 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.

Reasons to have chorionic villus sampling:

Chorionic villus sampling will usually tell you whether your baby will be born with any of the conditions that were tested for.

If no problem is found, it may be reassuring. If a condition is detected, you’ll have plenty of time to decide how you want to proceed with your pregnancy.

Read more about the results of chorionic villus sampling for more information.

Reasons not to have chorionic villus sampling:

There’s a 0.5 to 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.

Is chorionic villus sampling painful?

Chorionic villus sampling is usually described as being uncomfortable, rather than painful.

In most cases, an injection of local anesthetic will be given before transabdominal chorionic villus sampling to numb the area where the needle is inserted, but you may have a sore tummy afterwards.

Transcervical chorionic villus sampling feels similar to a Pap screening test.

Chorionic villus sampling vs Amniocentesis

Chorionic villus sampling is an alternative to amniocentesis, where a sample of the mother’s amniotic fluid is taken for testing. Chorionic villus sampling can be carried out earlier than amniocentesis, which is usually carried out between weeks 15 and 20 of pregnancy.

Results from amniocentesis can take 2 to 3 weeks to come through. This may mean that your pregnancy is at a more advanced stage, around 20 weeks or more, before you can consider the results.

If you are at risk of passing a genetic condition on to your child, your doctor or midwife will be able to discuss the tests with you and explain why they might be necessary. They can also help you make a decision, if needed, about whether to continue with your pregnancy.

In some cases, you may be referred to a genetic counselor (a healthcare professional trained in genetics). They will discuss your risk of passing on certain genetic conditions and can offer you advice about what to do when you get the results of chorionic villus sampling.

Preparing for chorionic villus sampling

You won’t usually need to do anything special to prepare for chorionic villus sampling. You can eat and drink as normal beforehand.

In some cases, you may be asked to avoid going to the toilet for a few hours before having chorionic villus sampling, because it’s sometimes easier to do the test when your bladder is full. Your doctor or midwife will tell you about this before you attend your appointment.

You may want to bring a partner, friend or family member for support when you have the test.

Chorionic villus sampling procedure

A health care provider with expertise in performing chorionic villus sampling takes a tiny piece of tissue from the placenta, which has cells from your 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.

During chorionic villus sampling, a sample of cells, called ‘chorionic villi cells’, is taken from your placenta using one of the procedures below:

1. Transabdominal chorionic villus sampling — Your abdomen is cleaned with antiseptic before a local anesthetic injection is used to numb it. A needle is inserted through your abdomen, observed at all times by ultrasound. The needle does not enter the amniotic sac or go near the baby. The procedure is performed under local anesthetic. A syringe is attached to the needle, which is used to take a small sample of cells from the chorionic villi. After the sample is removed, the needle is removed.
2. Transcervical chorionic villus sampling — A tube is inserted through your cervix (the neck of the womb) and observed by ultrasound. You don’t need an anesthetic — it’s similar to having a Pap smear. The tube gently sucks in a tiny sample of the placenta tissue. Some women who have testing through the cervix say it feels like having a Pap smear.

The test takes about 5 minutes, although the whole consultation will take about 30 to 45 minutes. Some women find that chorionic villus sampling is painless. Others described chorionic villus sampling as uncomfortable rather than painful, and there may be some cramps afterwards which are similar to menstrual cramps.

After chorionic villus sampling, 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.

Chorionic villus sampling 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.

Which method will be used?

In most cases, the transabdominal method is preferred in most cases, because it’s often easier to carry out.

Transcervical chorionic villus sampling is also more likely to cause vaginal bleeding immediately after the procedure, which occurs in about 1 in 10 women who have this procedure. There is, however, no difference in the rate of miscarriages between the 2 methods.

Transcervical chorionic villus sampling may be preferred to transabdominal chorionic villus sampling if it’s easier to reach your placenta this way.

Chorionic villus sampling recovery

After having chorionic villus sampling, it’s normal to have cramps similar to period pain and light vaginal bleeding called “spotting” for a day or two.

You can take painkillers you can buy in a pahrmacy or shop, such as paracetamol (but not ibuprofen or aspirin), if you experience any discomfort.

You may wish to avoid any strenuous activity for the rest of the day.

Contact your midwife or the hospital where the procedure was carried out for advice as soon as possible if you develop any of the following symptoms after the procedure:

• persistent or severe pain
• a high temperature of 100.4 °F (38 °C) or more
• chills or shivering
• heavy vaginal bleeding
• discharge of clear fluid from your vagina
• contractions

Getting the chorionic villus sampling results

After chorionic villus sampling has been carried out, the sample of chorionic villi will be taken to a laboratory so that the cells can be examined under a microscope. The number of chromosomes in the cells can be counted, and the structure of the chromosomes can be checked for any abnormalities. If the chorionic villus sampling is being carried out to test for a specific genetic disorder, the cells in the sample can also be tested for this. Chorionic villus sampling is estimated to be about accurate in 99 cases out of 100.

However, chorionic villus sampling cannot test for every birth defect, and it may not give conclusive results. In about 1 of every 100 cases, the results of chorionic villus sampling cannot be completely certain that the chromosomes in the fetus are normal. If this happens, it may be necessary to have further tests, such as examining the chromosomes in cells from the parents. It may also be necessary to have amniocentesis (an alternative test in which a sample of amniotic fluid is taken from the mother) to confirm a diagnosis.

The first result should be available within a few days, and this will tell you whether a major chromosome problem has been discovered. The full results, including smaller, rarer conditions, can take 2 to 3 weeks to come back, although if the test is looking for a specific disorder the results may take up to a month. For most women who have chorionic villus sampling, the results of the procedure will be ‘normal’. This means the baby will not have any of the disorders that were tested for.

It is occasionally possible to have a normal result but then the baby is born either with the condition that was tested for or with another genetic condition. This is because a normal test result cannot exclude every possible genetic disorder. If your test is ‘positive’, your baby has the disorder that was being tested for. You will then be able to discuss the implications fully. There is no cure for most chromosomal conditions. A baby born with one of these conditions will always have the condition, so you’ll need to consider your options carefully. Therefore, you need to consider your options carefully.

These will include:

• continuing with your pregnancy, while gathering information about the condition so that you are prepared for caring for your baby
• terminating the pregnancy

If you are considering termination, talk to your doctor or midwife. They can give you important information and advice and can refer you to a counselor if you like. This can be a very difficult decision, but you don’t have to make it on your own.

Talk to your doctor about the meaning of your specific test results. Ask your doctor:

• How the condition or defect may be treated either during or after the pregnancy
• What special needs your child may have after birth
• What other options you have about maintaining or ending your pregnancy

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

Chorionic villus sampling risks

Chorionic villus sampling increases your risk of miscarriage, but only 1 in every 100 pregnancies that end in miscarriage would be directly due to chorionic villus sampling. This risk is in addition to the ‘background risk’ of miscarriage that all women have in early pregnancy due to natural causes. It is important to discuss your risk of miscarriage with your doctor, midwife or genetic counselor.

The specific figure for the risk of a miscarriage depends on the experience of the doctor doing the test and the difficulty he or she has in obtaining the sample. It is therefore important that a chorionic villus sampling test is only carried out by a doctor experienced in this technique and it should be done after the 11th week of pregnancy.

Possible complications chorionic villus sampling include:

• Bleeding
• Infection
• Miscarriage (in up to 1 in 100 women)
• Rh incompatibility in the mother
• Rupture of membranes

You may have some vaginal bleeding after a chorionic villus sampling. Talk to your doctor about what you can expect after the testing and what symptoms to look out for.

If your blood is Rh negative, you may receive a medicine called Rho(D) immune globulin (RhoGAM and other brands) to prevent Rh incompatibility.

You will receive a follow-up ultrasound 2 to 4 days after the procedure to make sure your pregnancy is proceeding normally.