Birth Defects Testing

Types of Tests

You and your doctor can choose from several tests. What you choose depends on your wishes, where you are in your pregnancy, your family health history, and what tests are available in your area. You may have no tests, one test, or several tests.

Screening tests show the chance that a baby has a certain birth defect. Diagnostic tests show if a baby has a certain birth defect.

First-Trimester Tests

Screening tests

The nuchal translucency test and the first-trimester blood tests are often done together in what is called the first-trimester screening.

• Nuchal translucency test. This test uses ultrasound to measure the thickness of the area at the back of the baby's neck. An increase in the thickness can be an early sign of certain birth defects, such as Down syndrome. This test is often done along with blood tests in the late first trimester. It is not available everywhere, because a doctor must have special training to do it.
• First-trimester blood tests. These tests measure the amounts of two substances in your blood: beta human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein A (PAPP-A). Beta-hCG is a hormone made by the placenta. High levels may be related to certain birth defects. PAPP-A is a protein in the blood. Low levels may be related to certain birth defects. The doctor looks at the test results—along with your age and other factors—to find out the chance that your baby may have certain problems.

First-trimester tests also can be done as part of an integrated screening test. This test combines the results of the first-trimester tests (first-trimester blood tests and nuchal translucency test) with those of a second-trimester test (the triple or quad screening).

Cell-free fetal DNA

The cell-free fetal DNA test looks at fetal DNA in a pregnant woman's blood. It can help find genetic problems like Down syndrome or trisomy 18. This test is an option for women who have risk factors for having a baby with certain birth defects. It's not used as a general screening test or for women who are carrying twins.

Diagnostic test

• Chorionic villus sampling (CVS) . Doctors can use this test to look at cells in the placenta. CVS can be done between 10 and 13 weeks of pregnancy. A doctor collects a sample of chorionic villus cells by putting a thin flexible tube (catheter) into your uterus through your vagina or by putting a needle through your belly into your uterus. The test can be used to find chromosomal birth defects such as Down syndrome and family diseases such as sickle cell disease or cystic fibrosis. But it cannot find neural tube defects.

Second-Trimester Tests

Screening tests

• Triple or quadruple (quad) blood tests . These tests check the amounts of three or four substances in a pregnant woman's blood. The triple screen checks the levels of alpha-fetoprotein (AFP), beta human chorionic gonadotropin (beta-hCG), and a type of estrogen(estriol, or uE3). The quad screen checks those three substances, plus the level of the hormone inhibin A. The doctor looks at these test results—along with your age and other factors—to find out the chance that your baby may have certain problems. Second-trimester tests can be done between 15 and 20 weeks of pregnancy. The triple and quad blood tests may be called the expanded AFP test, the AFP plus test, or the multiple marker screening test. Either of these tests may be done as the second part of the integrated screening test.
• Ultrasound . This test allows your doctor to see an image of your developing baby. It is often done at 18 to 20 weeks of pregnancy. Doctors can use ultrasound to look for certain features that are related to some problems, such as Down syndrome. The test also can be used to find problems of the heart, spine, belly, or other areas.

Diagnostic test

• Amniocentesis . Doctors use this test to look for chromosomal problems in the baby's cells. A doctor puts a needle through the belly and into the uterus to collect some of the amniotic fluid that surrounds the baby. This fluid contains some of the baby's cells. The test is done between 15 and 20 weeks of pregnancy, usually around week 16. This test also can help find neural tube defects, such as spina bifida.

Deciding About Testing

The decision to have a test for birth defects is personal. You have to think about your age, your chance of passing on a family disease, your need to know about any problems, and what you might do after you have the test results. Your spiritual beliefs and other values also may play a role in your decision.

Some birth defects—such as a cleft lip or cleft palate or certain heart problems—can be fixed with surgery after birth and sometimes even with surgery during pregnancy. Some other defects cannot be fixed.

Reasons to have tests

You may decide to have the tests because:

• You would think about whether to continue the pregnancy if there is a birth defect.
• You have a family history of an illness such as cystic fibrosis, Tay-Sachs disease, or hemophilia. To learn more about cystic fibrosis testing, see the topic Cystic Fibrosis Carrier Screening.
• You have insurance that will pay for some or all of the cost of the tests.
• You need to know whether there might be a problem, because not knowing would make you worry.
• You want to learn all you can about caring for and raising a child with a certain birth defect.
• You would want to plan what hospital and doctors to work with to make sure that all of your baby's needs are met.

Reasons NOT to have tests

You may decide not to have birth defects tests because:

• You would continue the pregnancy no matter what the tests show.
• The screening test may show an increased risk for a problem even though your baby doesn't have the problem. You would be worried while you wait for the test results.
• These tests can't find all possible problems.
• You are worried about the risk of miscarriage. Both CVS and amniocentesis have a small risk of miscarriage.
• Tests can be expensive. You may not have insurance, or your insurance may not pay for the tests.