Maternal serum alpha-fetoprotein at 12, 22 and 32 weeks' gestation in screening for pre-eclampsia

Objective To examine the distribution of maternal serum alpha-fetoprotein (AFP) at 12, 22 and 32 weeks' gestation in singleton pregnancies which develop pre-eclampsia (PE) and examine the performance of this biomarker in screening for PE. Methods Serum AFP was measured in 17 071 cases at 11-13 weeks, in 8583 cases at 19-24 weeks and 8609 cases at 30-34 weeks' gestation. Bayes' theorem was used to combine the a-priori risk from maternal characteristics and medical history with AFP. The performance of screening for PE requiring delivery < 32, at 32 + 0 to 36 + 6, < 37 and >= 37 weeks' gestation was estimated. Results In pregnancies that developed PE, serum AFP multiples of the median (MoM) was increased at 11-13 and 19-24 weeks' gestation, but not at 30-34 weeks, and the values were inversely related to gestational age at delivery. Combined screening with maternal factors and serum AFP improved the prediction provided by maternal factors alone for PE delivering < 37 weeks, but not for PE delivering >= 37 weeks. The performance of screening for preterm PE was better at 19-24 weeks than at 11-13 weeks and the detection rate (DR) for a given false-positive rate (FPR) was higher for PE delivering < 32 weeks than for PE delivering at 32 + 0 to 36 + 6 weeks. The DRs, at 10% FPR, of combined screening at 11-13 weeks for PE delivering < 32 and at 32 + 0 to 36 + 6 weeks were 54% and 45%, respectively, and these improved to 72% and 53% with screening at 19-24 weeks. Conclusions Measurement of serum AFP at 11-13 and 19-24 weeks' gestation improves the prediction of preterm PE provided by maternal factors alone. Copyright (C) 2015 ISUOG. Published by John Wiley & Sons Ltd.