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.
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.
Pregnant women and their partners can choose whether to
have a test for birth defects. 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.
Deciding about testing 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.
Health Tools help you make wise health decisions or take action to improve your health.
Decision Points focus on key medical care decisions that are important to many health problems.
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.
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.
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.
Triple or quadruple (quad) blood tests. These tests check the amounts of three or four substances in a pregnant woman’s
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.
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.
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
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
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
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.
American College of Obstetricians and Gynecologists (2015). Cell-free DNA screening for fetal aneuploidy. ACOG Committee Opinion No. 640. Obstetrics and Gynecology, 126(3): 691-692. DOI: 10.1097/01.AOG.0000471171.86798.ac. Accessed April 11, 2017.
American College of Obstetricians and Gynecologists (2016). Prenatal diagnostic testing for genetic disorders. ACOG Practice Bulletin No. 162. Obstetrics and Gynecology, 127(5): e108-e122. DOI: 10.1097/AOG.0000000000001405. Accessed April 6, 2017.
Wapner RJ, et al. (2009). Prenatal diagnosis of congenital disorders. In RK Creasy et al., eds., Creasy and Resnik’s Maternal-Fetal Medicine: Principles and Practice, 6th ed., pp. 221-274. Philadelphia: Saunders Elsevier.
ByHealthwise Staff Primary Medical ReviewerSarah Marshall, MD – Family Medicine Adam Husney, MD – Family Medicine Kathleen Romito, MD – Family Medicine Elizabeth T. Russo, MD – Internal Medicine Specialist Medical ReviewerSiobhan M. Dolan, MD, MPH – Reproductive Genetics