Study on the use of second trimester maternal serum screening for Down's syndrome.

Objective: To establish gestational age - specific Serum AFP and free - 3 - HCG level medians of pregnant women in our screening population. Methods: The level of maternal serum Alpha - fetoprotein and beta - hCG were measured with full automatic chemiluminescence immunoassay system at 14 -22 weeks' gestation. Down's syndrome risk value was calculated with Multicalc Software with cut off value at 1: 380. The high risk rates screened in different gestational age - groups were compared. Results: 1825 pregnant women received biochemical marker screening. 101 out of 1825 were found at high risk of Down syndrome (5. 5 % ). False positive rate was 5. 4%. No false negative case found in this study population. Amniocentesis was conducted in 41 of 101. 2 cases with fetal chromosome abnormalities were detected. The medians of serum level of AFP and free β - HCG were established with maternal weight correction. The significant differences between established medians and the original Gaussian ones were found. The high risk rate present uptrend with age. Conclusions: Maternal serum screening was effective means to defect fetal chromosome abnormalities. It is necessary to establish the median of AFP, BBB - HCG in Chinese population.