Topic Overview

What are birth defects tests?

Birth defects tests are done during pregnancy to look for possible problems with the baby (fetus). Birth defects develop when something is wrong with genes or chromosomes, an organ, or body chemistry. A birth defect may have only a mild impact on a child's life, or it can have a major effect on quality of life or life span.

Birth defects include:

• Genetic disorders, such as Down syndrome and trisomy 18.
• Diseases passed in a family, such as Tay-Sachs, sickle cell anemia, and cystic fibrosis.
• Structural problems, such as heart defects and neural tube defects, including spina bifida.

What are the types of tests?

There are two types of birth defects tests: screening and diagnostic.

• Screening tests show the chance that a baby has a certain birth defect. It can't tell you for sure that your baby has a problem. If the test result is "positive," it means that your baby is more likely to have that birth defect. So your doctor may want you to have a diagnostic test to make sure. If the screening test result is "negative," it means that your baby probably doesn't have that birth defect. But it doesn't guarantee that you will have a normal pregnancy or baby.
• Diagnostic tests show if a baby has a certain birth defect.

Screening tests for birth defects are blood tests and ultrasounds. The blood tests are used to look for the amount of certain substances in your blood. The doctor uses an ultrasound to look for certain changes in the baby. Diagnostic tests involve taking some of the baby's cells to look at the genes and chromosomes.

No test is 100% accurate. A test may be negative even when the baby has a birth defect. This is called a false-negative test result. It's also possible that a test will be positive—meaning the test result is abnormal—but the baby does not have the problem. This is called a false-positive test result.

You may have only first trimester tests or only second trimester tests. Or you may have an integrated test. This test combines the results of tests you have in your first trimester and second trimesters.

Should you have birth defects tests?

Pregnant women and their partners can choose whether to have a test for birth defects. It can be a hard and emotional choice. You need to think about what the results of a test would mean to you and how they might affect your choices about your pregnancy.

For example, you may want to have tests to know if there is a problem so you can work with a doctor and hospital to care for your baby after birth. Or you may want to have tests because you wouldn't want to continue the pregnancy if there is a serious problem. Some women might decide not to have these tests because they would continue the pregnancy regardless of the results.

Talk to your doctor about tests that are available where you live and which tests might be best for you.

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