CHICAGO --- First-trimester tests for two proteins in the blood of pregnant women, combined with ultrasonography measurements of fetal neck skin, may provide the earliest diagnosis yet of fetal birth defects in at-risk women. The combined-risk assessment method has an estimated detection rate of Down syndrome of about 90 percent and is completely non-invasive.
Northwestern University Medical School researchers are evaluating the combined-risk assessment method, factoring in duration of pregnancy and maternal age at the time of screening, to determine the test's value in predicting fetal abnormalities. The National Institutes of Health-sponsored study also will assess if such a screening system could be implemented nationwide.
"Overall, we may end up with an earlier test (first vs. second trimester), with a higher detection rate (90-plus percent vs. 60 percent), doing less-invasive procedures and losing fewer normal pregnancies than might have been lost as a direct consequence of invasive procedures," said Eugene Pergament, M.D., lead investigator on the study, who is a professor of obstetrics and gynecology at the Medical School and director of reproductive genetics at Northwestern Memorial Hospital.
Birth defects such as Down syndrome occur more commonly in pregnancies in women aged 35 and older. For women at advanced maternal age, two procedures, chorionic villus sampling (CVS) in the first trimester (first 12 weeks of pregnancy) and amniocentesis in the second trimester (12 to 24 weeks of pregnancy), are offered. The accuracy of CVS and amniocentesis is very close to 100 percent. However, both procedures carry a risk of losing the pregnancy because they are invasive.
CVS uses either a catheter placed in the placenta through the cervix or a needle placed in the placenta through the abdomen. Amniocentesis is similar to CVS because it is performed with a needle inserted through the abdomen.