Higher Median Levels of Free -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 -hCG and PAPP-A in the fi rst trimester of pregnancy. Methods: The data of 943 women undergoing fi rst trimester combined screening for fetal Down syndrome were analysed to derive the Chinese-specifi c medians. The calculated risk of Down syndrome based on these Chinese-specifi c 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 -hCG and PAPP-A were signifi cantly higher among the Chinese than among the Caucasians. The weight-adjusted gestation-specifi c 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 signifi cantly higher maternal serum level of free -hCG and PAPP-A Received: October 15, 2004 Accepted after revision: January 26, 2005