What the results mean and what comes next
If your first-trimester screening is positive, you may want to follow up with one of two older procedures—chorionic villus sampling (CVS) or amniocentesis. Both can determine with nearly 100 percent accuracy whether the fetus has Down syndrome. With CVS, which can be performed in the first trimester, a needle is inserted into the uterus to obtain a sample of the placenta. Amniocentesis, which involves using a needle to extract amniotic fluid for analysis, cannot be performed until at least week 15.
Done properly, both procedures pose only a small risk of miscarriage or other problems. “When performed by an experienced doctor, the procedure-related risk of amnio and CVS is about one in 400,” Simpson says. (Ideally, your physician should have done several hundred or more of these procedures.)
Researchers are divided on whether women should receive both first- and second-trimester Down syndrome tests. In research D’Alton conducted, doing so yielded the highest detection rate ever for a noninvasive test—94 percent—but the false-positive rate was 11 percent.
However, waiting for confirmation in the second trimester eliminates the first trimester test’s main advantage. “If a woman decides to terminate her pregnancy, doing so in the first trimester offers her greater privacy and access to a provider,” Simpson says. “Waiting until later increases risk of complications—and even maternal death—tenfold.”
For more information on prenatal testing, go to www.fitpregnancy.com/yourpregnancy/89