New guidelines recommend offering all expectant women the choice to have screening and diagnostic testing for Down syndrome, an option previously recommended only for some pregnant women based on age and other risk factors. Down syndrome, which affects 1 in every 800 live infants (most embryos with Down syndrome are spontaneously lost during pregnancy), occurs when extra genetic material causes delays in the way a child develops, resulting in mental retardation, differences in physical features, and often other birth defects and health problems.
The new testing guidelines come from the American College of Obstetricians and Gynecologists (ACOG), and were published in the January 2007 edition of Obstetrics & Gynecology. Before, genetic counseling and diagnostic testing for Down syndrome were only offered to pregnant women 35 and older, those with a family history of genetic defects, or those who had an abnormal result on a screening test.
The new guidelines recommend that all pregnant women should be offered early, less invasive screening options, which include both a blood test and a nuchal translucency (NT) test. Typically performed between weeks 11 and 14 of pregnancy, an NT test uses ultrasound to measure the clear-appearing space in the folds of tissue behind a developing baby's neck. In babies with Down syndrome and certain other chromosomal abnormalities, the space appears larger than normal.
Under the new guidelines, if tests show an increased risk of the fetus having Down syndrome, pregnant women of all ages can then choose to have genetic counseling and follow-up diagnostic testing.
Diagnostic tests used to assess a woman's risk of having a baby with Down syndrome include amniocentesis (also called an amnio) and chorionic villus sampling (CVS). Although these are accurate in detecting Down syndrome and other chromosomal abnormalities, amnio and CVS are associated with a small risk of miscarriage and other complications. Both of the tests are performed by inserting a needle through the abdomen into the uterus — an amnio removes a small amount of amniotic fluid and a CVS takes a tiny sample of the placenta.
The difference between a screening test and a diagnostic test is that screening tests only reveal the possibility that a problem might exist, whereas diagnostic tests can determine — with a fair degree of certainty — whether a fetus actually has a specific problem.
What This Means to You
It's your decision which tests to have during your pregnancy — no test is mandatory. Talk to your doctor about what tests are available and appropriate for you. Also find out:
- what the tests look for
- what the risks and benefits are
- how accurate they are (especially what the results will — and won't — tell you)
Prenatal tests aren't always definitive. Because many women with abnormal test results end up having healthy babies and a number of the problems that are detected can't be treated, some women decide not to undergo testing. Another factor in a woman's decision about testing is whether or not she would consider terminating the pregnancy if she learns she is carrying a fetus with a serious birth defect.
If you're interested in screening for Down syndrome, you'll need to have it done by the 20th week of your pregnancy. If tests show that you are at increased risk of having a baby with Down syndrome, your doctor or a genetic counselor can give you the facts and answer your questions.
Reviewed by: Steven Dowshen, MD
Date reviewed: January 2007
