Medians for Second-Trimester Down Syndrome Screening in Tianjin

Objective: To establish medians for second trimester Down syndrome screening in Tianjin district,and its clinical values thereof.Methods: The serum levels of maternal serum alpha-fetoprotein(AFP) and free human chorionic go nadotropin(Free β-hCG) from 113,544 pregnancies ranged from 14 weeks to 20+6 weeks were detected using time-resolved fluoroimmunoassay.The Medians Tool of the PE risk assessment software(LC3.0) was used to determine medians value of se rum AFP and free β-hCG in 61,881 pregnant women,which was modified by median coefficients,and established the Weight equation.The serum levels of AFP and free β-hCG were adjusted by median shift to establish median value system for sec ond-trimester Down syndrome screening in 38,662 pregnant women of the Tianjin area.The serum levels of AFP and free β-hCG were measured in other 13,001 pregnant women.The screening results were calculated using the standard algorithm based on the Caucasian median value system and the Tianjin median value system.Patients with an increased risk of Down syndrome pregnancy(≥270) were offered genetic amniocentesis.Results: Medians from 13,001 pregnant women matched the established median formula.The correction factors(Median factor) of AFP and free β-hCG were 1.01 and 1.00 respective ly.The detection rate(DR) of the Tianjin median value system for second-trimester Down syndrome screening was 77.78%,the false positive rate(FDR) was 5.33%,the positive predictive value was 1%,and the DR based on the Caucasian median val ue system was 77.78%,the FDR was 8.30%,the positive predictive value was 0.65%.Conclusion:Ethnic variance of mater nal serum levels of AFP and Free β-hCG exists between the Caucasian and Tianjin populations.The accuracy of screening is increased by using race-specific medians.