The importance of the trisomy 21 local cutoff value evaluation for prenatal screening in the second trimester of pregnancy.

Objective The aim of this work was to compare different local cutoff values (LCV) and inline cutoff values (ICV) in pregnant women in the second trimester at high risk for carrying fetuses with trisomy 21. Methods This retrospective cohort study analyzed prenatal screening outcomes in pregnant women (n = 311,561). The receiver operating characteristic curve was used to evaluate the diagnostic significance of the trisomy 21 risk value, alpha-fetoprotein, and free beta human chorionic gonadotropin multiple of the median for predicting trisomy 21 risk. The cutoff value corresponding to the maximal Youden index was taken as the LCV. The screening efficiency of both cutoff values was compared. Results The LCV cutoff value was lower than the ICV cutoff value (1/643 vs 1/270). The sensitivity increased by 19.80%, the positive predictive value decreased by 0.20%, and the false-positive rate increased by 6.50%. Conclusion The LCV should be used to determine trisomy 21 risk, which can increase the detection rate of trisomy 21 in the second trimester. [ABSTRACT FROM AUTHOR]