Medians For Second-Trimester Down Syndrome Screening In Tianjin

ObjectiveTo establish the median values system of maternal serum alpha-fetoprotein (AFP) and free human chorionic gonadotropin (Free β-hCG) for second trimester Down syndrome screening in Tianjin district, in order to discuss its clinical medical value.MethodWe measured serum level of AFP and Free β-hCG from100324pregnancies ranged from15weeks to20+6weeks using time-resolved fluoroimmunoassay. The Medians Tool of the PE risk assessment software (LC3.0) was used to determine61781pregnancies’ serum AFP and free β-hCG medians value. We modified the coefficients of the Median equation and Weight equation.38543pregnancies’serum AFP and free β-hCG levels were adjusted by median shift to establish median values system for second-trimester Down syndrome screening. Other13001pregnancies’ serum AFP and free β-hCG levels were measured. The screening results were calculated using the standard algorithm based on the Caucasian median values system and the Tianjin median value system. Patients with an increased risk of Down syndrome pregnancy (≥270) were offered genetic amniocentesis.Result1. The MOM medians of maternal serum alpha-fetoprotein (AFP) and free human chorionic gonadotropin (Free β-hCG) from15to20+6weeks of pregnancy are0.99to1.02and0.97to1.05respectively, and the body mass correction factor in the Tianjin median values system are0.71to1.20and0.68to1.23respectively. While in the Caucasian median values system the MOM medians of maternal serum alpha-fetoprotein (AFP) and free human chorionic gonadotropin (Free β-hCG) from15to20+6weeks of pregnancy are1.00to1.07and1.16to1.20respectively, and the body mass correction factor are0.76to1.27,0.65to1.25.2. The medians from13001pregnancies matched the established median formula. The Correction factor (Median factor) of AFP and free β-hCG were1.01and1.00 respectively. The Medians from13001pregnancies matched the established median formula, and the calibration curves of body mass are matched.3. The detection rate (DR) of the Tianjin median values system for second-trimester Down syndrome screening was77.78%, false positive rate (FDR) was5.33%, positive predictive value was10.00%o, and the DR based on the Caucasian median values system was77.78%, the FDR was8.30%, positive predictive value was6.49%o. It needs154cases of amniocentesis to detect one case of Down syndrome in the Caucasian median values system, and it needs just100cases of amniocentesis to detect one case of Down syndrome in the Tianjin median values system.Conclusion1. The Tianjin median values system is stable and reliable.2. It can effectively reduce the false positive rate and increase the positive predictive value by using the Tianjin median values system.