Higher median levels of free beta-hCG and PAPP-A in the first trimester of pregnancy in a Chinese ethnic group. Implication for first trimester combined screening for Down's syndrome in the Chinese population

Objective: To study the effect of ethnic Chinese on the medians of free beta-hCG and PAPP-A in the first trimester of pregnancy.

Methods: The data of 943 women undergoing first trimester combined screening for fetal Down syndrome were analysed to derive the Chinese-specific medians. The calculated risk of Down syndrome based on these Chinese-specific medians was compared with that based on the original algorithm of the Fetal Medicine Foundation (FMF).

Results: The maternal serum levels of multiples of median of free beta-hCG and PAPP-A were significantly higher among the Chinese than among the Caucasians. The weight-adjusted gestation-specific medians were developed. Without adjustment for ethnicity, the original FMF algorithm underestimated the risk of Down syndrome by a median of 1%. Adjustment by ethnicity increased the false-positive rate by 10% (from 5.3 to 5.9%).

Conclusion: Ethnic Chinese have a significantly higher maternal serum level of free beta-hCG and PAPP-A in the first trimester, which could not be explained by differences in maternal weight. Adjustment for ethnicity may be necessary for these biochemical markers in a first trimester screening program.