Prenatal diagnostic testing: Amniocentesis and CVS

Prenatal diagnostic testing can provide important information about your baby’s health during pregnancy. Tests like amniocentesis and chorionic villus sampling (CVS) help detect certain genetic conditions and birth defects early. Understanding these options can help you make informed decisions and feel more prepared throughout your pregnancy journey.

Some parents have increased risk of having a baby with a genetic disorder or other problem. They may want to consider one of these tests. Knowing about problems before the baby is born may help parents. They may be able to make better decisions about health care for their infant. Doctors can treat certain problems before the baby is born. Other problems may need special treatment right after delivery. In some cases, parents may even decide not to continue the pregnancy.

Doctors don’t require parents to have amniocentesis and chorionic villus sampling. Discuss the options with your doctor.

Path to improved health

Doctors perform amniocentesis or CVS when they determine there is an increased risk that the baby may have genetic disorders or birth defects, such as:

• You are 35 years of age or older by the time your baby is due. Mothers in this age group have increased risk of having a baby with a chromosome abnormality. This could include Down syndrome.
• You had a screening test that showed there could be a problem.
• You have had a child with Down syndrome, spina bifida, or other disorder.
• You or your partner is a known carrier of a genetic disorder, such as cystic fibrosis.

Before either procedure, you may have counseling with a genetic expert. This allows you to learn about the conditions the test may find. You will have a better idea of what those mean for you and your baby.

How is amniocentesis performed?

In this procedure, your doctor removes a sample of amniotic fluid (the fluid around your baby) from your uterus. The doctor inserts a long, thin needle through your abdomen into the uterus and withdraws a small amount of fluid. A laboratory then evaluates the fluid. Lab technicians can test it for:

• Genetic abnormalities
• Infection
• Signs of lung development

Your body will produce more fluid to replace the fluid the doctor removes. The procedure will not harm the baby. Some women feel mild cramping during or after the procedure. Your doctor may tell you to rest on the day of the test. Usually, you can resume normal activity the next day.

How is CVS performed?

CVS removes a small sample of placenta tissue from the uterus. The sample is then sent to the lab for testing. The sample can be taken 2 ways:

• A catheter (thin tube) through the vagina. The catheter is inserted into the vagina. It is passed through the cervix and into the uterus. The doctor uses images from an ultrasound to guide the catheter to the best spot for sampling.
• A needle through the abdomen. The sample can also be obtained by inserting a needle into the abdomen. The needle then withdraws placenta tissue. Again, ultrasound is used to guide the needle.

Local anesthesia is used for this test to reduce pain and discomfort. Most women feel fine after the test. Some may have mild bleeding (spotting) afterward.

When are the tests performed?

Amniocentesis is usually performed during the 15th week of pregnancy or later. CVS is usually performed between the 10th and 13th weeks of pregnancy.

Is one test better than the other?

The main benefit of CVS is that it can be done earlier in the pregnancy. It’s very accurate in detecting genetic abnormalities. But it does not detect some things that amniocentesis does. These include:

• Neural tube defects (involving the spinal column or brain).
• Birth defects.
• Rh incompatibility (when the mother has Rh-negative blood and the baby has Rh-positive blood).

Amniocentesis might be the best option if:

• You previously had a baby with a neural tube defect.
• You or your partner have a neural tube defect.
• The results of other tests during your pregnancy have been abnormal. This could include a blood screening test done in early pregnancy.

CVS may be better if you and your doctor want to know the test results during your first trimester.

Things to consider

Amniocentesis and CVS carry a few small risks. These include:

• Miscarriage
• Infection or injury to the baby
• Leaking of amniotic fluid
• Vaginal bleeding

The risks of CVS are slightly higher than for amniocentesis. Your doctor will talk to you about the risks and benefits of amniocentesis and CVS.

Questions for your doctor

• Am I at increased risk of having a baby with birth defects or genetic abnormalities?
• Do I need to get an amniocentesis or CVS?
• Which one would be better for me?
• What is the risk of miscarriage for each procedure?
• What are the complications?
• Will the procedure hurt?
• Is bleeding normal after the procedure?

Resources

March of Dimes: Amniocentesis

March of Dimes: Chorionic Villus Sampling

National Institutes of Health, MedlinePlus: Prenatal Testing