Fetal Down syndrome screening models for developing countries; Part I: Performance of Maternal Serum Screening

Background To identify the performance of fetal Down syndrome (DS) screening for developing countries. Methods A prospective study on MSS (maternal serum screening) with complete follow-ups (n = 41,924) was conducted in 32 network hospitals in the northern part of Thailand. Various models of MSS were tested for performance. Results MSS based on Caucasian reference range resulted in very high false positive rate (FPR; 13%) in our country, compared to the rate of 7.8% with our own (Thai) reference range, whereas the detection rate was comparable. As individual screening, C-S (contingent first trimester screening including PAPP-A, and free beta-hCG, classified as a) high risk [> 1:30], indicated for invasive diagnosis; b) intermediate risk [1:30-1500], indicated for STS; and c) low risk [< 1:1500], need no further tests.) was the most effective model (sensitivity 84.9%, FPR 7.7%) but nearly one-third needed the second trimester test (STS) because of intermediate results. Additionally, about one-third had their first visits in the second trimester and had no chance of FTS (first trimester screening). C-S plus STS had a sensitivity of 82.4% and FPR 8.1% whereas independent first and second trimester screening model (I-S) gave the sensitivity of 78.4% and FPR of 7.5% but was much more convenient and practical. Conclusion C-S plus STS was the most effective models while I-S model was also effective and may be better for developing countries because of its simplicity and feasibility.