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.