To examine the distribution of uterine artery pulsatility index (UtA-PI) at 12, 22, 32 and 36 weeks' gestation in singleton pregnancies which develop pre-eclampsia (PE) and examine the performance of this biomarker in screening for PE.Methods
UtA-PI was measured in 92 712 singleton pregnancies at 11–13 weeks, in 67 605 cases at 19–24 weeks, in 31 741 at 30–34 weeks and in 5523 at 35–37 weeks. Bayes' theorem was used to combine the a-priori risk from maternal characteristics and medical history with UtA-PI. The performance of screening for PE requiring delivery < 32, at 32 + 0 to 36 + 6, < 37 and ≥ 37 weeks' gestation was estimated. The results of combined screening were compared to those of screening by UtA-PI and by maternal factors alone.Results
In pregnancies that developed PE, UtA-PI was increased and the separation in multiples of the median (MoM) values from normal was greater with earlier, compared to later, gestational age at which delivery for PE became necessary. Additionally, the slope of regression lines of UtA-PI MoM with gestational age at delivery in pregnancies that developed PE increased with increasing gestational age at screening. The detection rate (DR), at a 10% false-positive rate (FPR), for PE delivering < 32 weeks was 71% and 88% with combined screening at 11–13 and 19–24 weeks, respectively, and the DR for PE delivering at 32 + 0 to 36 + 6 weeks was 52%, 63% and 71% with screening at 11–13, 19–24 and 30–34 weeks, respectively. However, the DR of PE delivering ≥ 37 weeks was only about 40%, irrespective of the gestational age at screening. The performance of screening by the approach utilizing Bayes' theorem was superior to that of using a percentile cut-off of UtA-PI for gestational age.Conclusions
The performance of combined screening with maternal factors and UtA-PI is superior for detection of early, compared to late, PE and, to a certain extent, improves with advancing gestational age at screening.