Please note: This information was current at the time of publication. But medical information is always changing, and some information given here may be out of date. For regularly updated information on a variety of health topics, please visit, the AAFP patient education website.

Information from Your Family Doctor

Prenatal Genetic Screening Tests


Am Fam Physician. 2009 Jan 15;79(2):124.

  See related article on fetal chromosomal abnormalities.

What are genetic screening tests?

They are tests to see if your baby is at risk of a genetic disorder, such as Down syndrome. Genetic disorders happen when your baby does not have the normal number of chromosomes, which contain the baby’s genes, or when there are problems with the brain or spine. Not all pregnant women have these tests. Your doctor will help you decide if these tests are right for you.

How does it work?

Some screening tests are done in the first trimester of pregnancy, and some are done in the second trimester. Your doctor may have you tested in both trimesters, depending on your baby’s risk and the testing method you select.

There are several ways to do the screening. One type of screening (no needles) is an ultrasound. This measures the thickness of the liquid under the skin on your baby’s neck. If the thickness is not normal, your baby may not have the normal number of chromosomes. Your doctor may also do a blood test to check your baby’s risk of having a genetic disorder.

There are two tests that can say for sure if your baby has a genetic disorder. They both have a small risk of causing a miscarriage. One test is called amniocentesis (AM-nee-oh-sen-TEE-sis). This is when the doctor uses a needle to take a small sample of fluid from the bag of water around the baby. The other test is called chorionic villus (core-ee-AH-nick VIL-us) sampling. This is when the doctor uses a needle to take a small sample of tissue from the placenta. This test is done earlier in the pregnancy than amniocentesis.

What should I do after I learn the results?

If the screening shows that your baby has a genetic disorder or is at risk of a genetic disorder, talk to your doctor about your options.

Where can I get more information?

Your doctor

American Academy of Family Physicians

Web site:

U.S. National Library of Medicine and the National Institutes of Health

Web site:

This handout is provided to you by your family doctor and the American Academy of Family Physicians. Other health-related information is available from the AAFP online at

This information provides a general overview and may not apply to everyone. Talk to your family doctor to find out if this information applies to you and to get more information on this subject.


Copyright © 2009 by the American Academy of Family Physicians.
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