Birth Defect and Genetic Testing During Pregnancy

Types of Tests

Testing may be done during pregnancy to look for possible birth defects and genetic conditions. These problems can include:

• Chromosome problems, such as Down syndrome and trisomy 18.
• Diseases that can be passed down in families, such as Tay-Sachs disease, cystic fibrosis, and sickle cell disease.
• Problems with the structure of an organ, including heart defects and neural tube defects, such as spina bifida.

There are two types of tests for birth defects and genetic conditions.

• Screening tests. These are blood tests and ultrasounds. These tests show the chance that a fetus has certain conditions.
• Diagnostic tests. These tests involve taking some cells from the fetus to look at the genes and chromosomes. They can show if a fetus has certain conditions.

A screening test can't tell you for sure that a fetus has a problem.

• If a screening test result is "negative," it means that the fetus probably doesn't have a certain condition. But it doesn't guarantee that you will have a normal pregnancy or a healthy baby.
• If a screening test is "positive," it means that the fetus is more likely to have a condition. So you may want to have a diagnostic test to make sure.

If you decide to have screening, you may have only first-trimester tests or only second-trimester tests. Or you may have an integrated screening test. This combines the results of first-trimester and second-trimester tests.

Your doctor or midwife can tell you which tests are available and which ones might be best for you.

It may not be easy to decide about testing for birth defects or genetic conditions. You may want to talk with a genetic counselor, who can discuss the reasons to have or not have a test. A counselor can also help you find other resources for support and decision-making.

Deciding About Testing

The decision to test for birth defects and genetic conditions during pregnancy is personal. There's a lot to think about, like what the results would mean to you, and how they might affect your choices.

Some conditions—like a cleft palate or certain heart problems—can be fixed with surgery after birth. But other conditions can't be fixed.

If you choose to have a test, you may want to talk with a genetic counselor. The counselor can talk with you about the reasons to have or not have the test. They can also help you find other resources for support and decision-making.

Birth defect and genetic testing

Here are some things to think about when deciding to test for birth defects or genetic conditions during pregnancy.

• Screening tests can't be used to diagnose a birth defect or genetic condition. They only estimate the chance that the fetus has a birth defect. If one of these tests shows a higher-than-normal chance of a problem, you would then decide whether to have a diagnostic test—such as chorionic villus sampling (CVS) in the first trimester or amniocentesis in the second trimester—to find out for sure if there is a problem.
• Screening tests correctly find most—but not all—cases of Down syndrome. But they sometimes show a higher risk for Down syndrome than is accurate (false-positive result).
• If you plan to have a diagnostic test such as CVS or amniocentesis, you can skip screening tests.
• Screening tests for birth defects and genetic conditions can't find every problem a fetus could have.

Early fetal ultrasound

Here are some things to think about when deciding about early fetal ultrasound screening.

• Fetal ultrasound is usually done during pregnancy to check the age, size, health, and position of the fetus. It is most often done at about 18 to 22 weeks. If you are sure of your last menstrual period and don't have any risk factors for birth defects, you may not need to have this test any earlier.
• Your doctor or midwife may recommend an early ultrasound if there's a need to find out exactly how long you have been pregnant, if you are having unusual symptoms such as bleeding, or if you have had abnormal results from another test.
• An early ultrasound may show a problem that goes away on its own or isn't important to your health or the health of the fetus. If that happens, you may need to have other tests to find if there really is a problem.
• Some "keepsake video" centers sell ultrasound videos as your baby's first photo. The U.S. Food and Drug Administration (FDA) does not recommend getting ultrasounds for this reason only. The FDA advises that keepsake images or videos only be made during an exam that's done for a medical reason and if no additional exposure is needed.

Chorionic villus sampling (CVS)

Here are some things to think about when deciding to have a CVS test.

• CVS is done in the first trimester. If the test shows a serious health problem, you have more time to decide whether you want to continue your pregnancy or prepare for care that may be needed.
• CVS isn't a routine test. But your doctor may recommend it if the chances of the fetus having a genetic condition are higher than average.
• Even though CVS can find certain problems, it can't guarantee that the fetus will be born healthy. No test can do that.
• CVS has some risks, including a small chance of causing a miscarriage.

Amniocentesis

Here are some things to think about when deciding to have an amniocentesis test.

• Your doctor or midwife may recommend this test if the chances of the fetus having a genetic condition or birth defect are higher than average.
• Even though amniocentesis can detect certain problems, it can't guarantee that your baby will be born healthy. No test can do that.
• If the test shows that the fetus may have a serious problem, you can decide whether you want to continue your pregnancy or prepare for care that may be needed.
• Amniocentesis is usually very safe. But it does have some risks, including a small chance of causing a miscarriage.

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