Objective

To examine the distribution of birthweight with gestational age in pregnancies complicated by preeclampsia (PE) and examine the potential value of sonographic estimated fetal weight (EFW) at mid-gestation as a predictor of PE.

Methods

The data for this study were derived from prospective screening for adverse obstetric outcomes in 93,911 women with singleton pregnancies attending for routine pregnancy care at 19+0 to 24+6 weeks’ gestation in two UK maternity hospitals. This visit included recording of maternal demographic characteristics and medical history, sonographic EFW and measurement of mean arterial pressure (MAP) and uterine artery pulsatility index (UtA-PI). The distribution of birthweight of the pregnancies with and without PE was assessed. The competing risks model was used to estimate the individual patient-specific risks of delivery with PE at <32 and <37 weeks’ gestation and at any gestation. The areas under the receiver operating characteristic (ROC) curve (AUC) and detection rates (DRs) of delivery with PE, at a 10% false positive rate (FPR), were assessed for various combinations of maternal risk factors EFW, MAP and UtA-PI. McNemar's test was used to determine the significance of difference in DR at 10% FPR in screening with and without EFW.

Results

The study population contained 2 843 (3.0%) pregnancies that subsequently developed PE, including 148 (0.2%) that delivered with PE at <32 weeks’ gestation and 654 (0.7%) that delivered with PE at <37 weeks. The birth weight was <10th percentile in 82% of pregnancies with PE delivering at <32 weeks’ gestation and this decreased to 21% for those with PE delivering at ≥37 weeks. In screening for delivery with PE at <32 and <37 weeks’ gestation, the DR at 10% FPR achieved by maternal risk factors (51% and 46%, respectively) was improved by addition of EFW (69% and 51%, respectively). Similarly, addition of EFW improved the performance of screening by a combination of maternal risk factors and MAP from 72% to 80% for PE <32 weeks and from 57% to 60% for PE <37 weeks. The EFW did not improve the predictive performance of screening by a combination of maternal risk factors, MAP and UtA-PI.

Conclusions

In pregnancies complicated by preterm-PE, a high proportion of babies are small for gestational age (SGA) and sonographic EFW at mid-gestation can improve the prediction of early and preterm-PE provided by maternal risk factors plus MAP, but not the prediction provided by a combination of maternal risk factors, MAP and UtA-PI.

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