DOWN-SYNDROME SCREENING IN AN ASIAN POPULATION USING ALPHA-FETOPROTEIN AND FREE BETA-HCG - A REPORT OF THE TAIWAN DOWN-SYNDROME SCREENING GROUP

Objective: To evaluate whether the strategy of maternal serum screenin g for Down syndrome, using alpha-fetoprotein (AFP) and free beta-hCG i n combination with maternal age, a technique developed in western coun tries, is applicable to an Asian population. Methods: Alpha-fetoprotei n and beta-hCG were measured in serum samples from 23 Down syndrome pr egnancies and 1748 unaffected singleton Taiwanese (ethnically Chinese) pregnancies at 14-22 weeks' gestation. Gestational age-specific media ns and a maternal weight correction formula were established for our o wn population. Likelihood ratio for Down syndrome pregnancies in relat ion to multiples of the median (MoM) levels of these analytes were der ived from the overlapping gaussian frequency distribution curves for D own syndrome and unaffected pregnancies. Results: The serum AFP and fr ee beta-hCG median MoM values of Down syndrome pregnancies were signif icantly abnormal in Asian subjects (0.77 and 2.91, respectively), and similar to those of affected pregnancies in white women. The median va lue of free beta-hCG:AFP MoM ratio (2.97) in Down syndrome pregnancies was significantly higher than that of unaffected pregnancies (1.09). The mean maternal weight during the second trimester in pregnant Asian women (55.2 kg) was markedly lighter than that of white women. At a 5 .8% false-positive rate, free beta-hCG identified 47.8% bf Down syndro me pregnancies (likelihood ratio 8.2), AFP detected only 13% of the ca ses (likelihood ratio 2.2), and free beta-hCG:AFP MoM ratio detected 4 3.5% of the cases (likelihood ratio 7.4). By using a multivariate risk algorithm involving the combination of AFP, free beta-hCG, and matern al age, 56.5% of Down syndrome cases could be detected with a 5.3% fal se-positive rate (likelihood ratio 10.7). Conclusion: Maternal serum s creening strategy using AFP and free beta-hCG in combination with mate rnal age is feasible in the detection of fetal Down syndrome among Asi an women.