A PRENATAL TRISOMY-21 SCREENING-PROGRAM USING ALPHA-FETOPROTEIN, HUMAN CHORIONIC-GONADOTROPIN, AND FREE ESTRIOL ASSAYS ON MATERNAL DRIED BLOOD

OBJECTIVE: The feasibility of large-scale Down syndrome maternal scree ning with dried blood samples and nonradioactive methods was examined. STUDY DESIGN: A prospective observation study was performed on a nons elected population of 11,241 pregnant women sampled between January 19 91 and September 1992, between 14 and 24 weeks' gestation (ultrasonogr aphic scanning available for 91.6%), through a multicenter collaborati ve network. Enzyme-linked immunosorbent assays for a-fetoprotein, huma n chorionic gonadotropin, and free estriol were performed on dried blo od samples. Risk determination was made with an in-house software impl ementing the multivariate gaussian log likelihood method.RESULTS: A to tal of 10,450 samples were eligible for the study. Mean age at term wa s 27.9 years. A total of 6.84% of the patients were greater than or eq ual to 35 years old with a prior risk of trisomy 21 > 1:350. The gener al positive rate of our sample was 8.15%. After calculation 31.7% with prior risk > 1:350 were still in the high-risk group; 6.36% of the lo w-risk group were found to be at high risk for Down syndrome. Fifteen trisomic pregnancies were observed, of which 11 had a calculated risk higher than the selected cutoff value (1:350). The overall detection r ate was 73%, specificity was 92%, and positive predictive power was 1. 2%. CONCLUSION: Our pilot study has shown performances within the rang e of conventional serum screening programs. Dried blood assays are a h andy alternative to serum assays. Blot paper cards represent a simple method of sampling, well fitted for large population screening. Combin ed with nonradioactive methods, this method appears to be both low cos t and effective. The current work apparently is the first large-scale Down screening program performed with dried blood.