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.
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. 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.
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
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 with those of a second trimester test (the triple or quad screening).
Chorionic villus sampling (CVS). Doctors
can use this test to look at cells in the placenta. CVS can be done between 10
and 12 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.
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. For more
information on 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 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.
For more help on deciding about tests, see the topics:
Centers for Disease Control and Prevention (CDC):
National Center on Birth Defects and Developmental Disabilities
1600 Clifton Road, MS E-87
Atlanta, GA 30333
NCBDDD aims to find the cause of and prevent birth
defects and developmental disabilities. This agency works to help people of all
ages with disabilities live to the fullest. The website has information on
many topics, including genetics, autism, ADHD, fetal alcohol spectrum
disorders, diabetes and pregnancy, blood disorders, and hearing loss.
Genetics Home Reference, U.S. National Library of
8600 Rockville Pike
Bethesda, MD 20894
The Genetics Home Reference provides information on hundreds of genetic conditions. The website has many tools for learning about human genetics and the way genetic changes can cause
disease. It also has links to additional resources for people who
have genetic conditions and for their families.
March of Dimes
1275 Mamaroneck Avenue
White Plains, NY 10605
The March of Dimes tries to improve the health of babies
by preventing birth defects, premature birth, and early death. March of Dimes
supports research, community services, education, and advocacy to save babies'
lives. The organization's website has information on premature birth, birth
defects, birth defects testing, pregnancy, and prenatal care.
American College of Obstetricians and Gynecologists (2007, reaffirmed 2009). Invasive prenatal testing for aneuploidy. ACOG Practice Bulletin No. 88. Obstetrics and Gynecology, 110(6): 1459–1467.
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.
How this information was developed to help you make better health decisions.