Assessment of risk for pre-eclampsia at mid-gestation to define subsequent care

Abstract

Objective: To stratify pregnancy care based on the estimated risk of pre-eclampsia (PE) from screening at 19-24 weeks' gestation by combinations of maternal risk factors, estimated fetal weight (EFW), mean arterial pressure (MAP) and uterine artery pulsatility index (UtA-PI).

Methods: The data for this study were derived from a prospective non-interventional study in 134 443 women with a singleton pregnancy attending for a routine ultrasound scan at 19 + 0 to 23 + 6 weeks' gestation in two UK maternity hospitals. The visit included recording of maternal demographic characteristics and medical history, sonographic EFW and measurement of MAP and UtA-PI. The competing-risks model was used to estimate the individual patient-specific risk of delivery with PE at < 28, < 32 and < 36 weeks' gestation. Receiver-operating-characteristics curves were constructed for screen-positive rates (SPRs) at different detection rates of delivery with PE at < 28, < 32 and < 36 weeks' gestation for the combinations of maternal risk factors, EFW and MAP, and of maternal risk factors, EFW, MAP and UtA-PI. Different risk cut-offs were used with the intention of detecting about 80%, 85% and 90% of cases of delivery with PE at < 28, < 32 and < 36 weeks' gestation. Calibration for risk of delivery with PE at < 28, < 32 and < 36 weeks' gestation was assessed by plotting the observed incidence of PE against the predicted incidence of PE.

Results: The study population contained 4335 (3.2%) women that subsequently developed PE, including 64 (0.05%) that delivered with PE at < 28 weeks' gestation, 209 (0.2%) that delivered with PE at < 32 weeks and 655 (0.5%) that delivered with PE at < 36 weeks. If the objective of screening was to identify about 90% of cases of delivery with PE at < 28, < 32 and < 36 weeks and the method of screening was a combination of maternal risk factors, EFW and MAP, the respective SPRs would be 11.0%, 18.3% and 38.8%. If the method of screening also included UtA-PI, the respective SPRs would be 2.6%, 3.8% and 23.6%. If the objective of screening was to identify about 80% of cases of delivery with PE at < 28, < 32 and < 36 weeks and the method of screening was a combination of maternal risk factors, EFW and MAP, the respective SPRs would be 5.9%, 9.7% and 21.9%. If the method of screening also included UtA-PI, the respective SPRs would be 1.0%, 2.1% and 11.7%. The calibration plots demonstrated good agreement between the estimated risk and observed incidence of PE.

Conclusions: All women should be offered assessment of risk for PE at 11-13 weeks, to help identify those requiring aspirin prophylaxis to reduce the rate of preterm PE, and at 35-37 weeks, to determine the optimal timing of birth to reduce the rate of term PE. Assessment of risk for PE at mid-gestation can be used to identify the subgroups that require additional monitoring at 24-35, 28-35 and 32-35 weeks' gestation. The best performance of screening, reflected in the SPR necessary to achieve a high detection rate, is achieved by a combination of maternal risk factors, MAP and UtA-PI. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Keywords: estimated fetal weight; fetal biometry; impaired placentation; mean arterial pressure; pre‐eclampsia; uterine artery Doppler.

Figure 1

Estimated fetal weight (EFW) Z‐score (a), mean arterial pressure (MAP) multiples of the median (MoM) (b) and uterine artery pulsatility index (UtA‐PI) MoM (c) at 19 + 0 to 23 + 6 weeks' gestation, plotted against gestational age (GA) at delivery with pre‐eclampsia (PE). Red lines are fitted relationships.

Figure 2

Receiver‐operating‐characteristics curves for prediction of delivery with pre‐eclampsia at (a) < 28 weeks, (b) < 32 weeks and (c) < 36 weeks' gestation, in screening by a combination of maternal risk factors with estimated fetal weight and mean arterial pressure. On top of each panel are the risk cut‐offs (i.e. 1 in…).

Figure 3

Receiver‐operating‐characteristics curves for prediction of delivery with pre‐eclampsia at (a) < 28 weeks, (b)< 32 weeks and (c) < 36 weeks' gestation, in screening by a combination of maternal risk factors with estimated fetal weight, mean arterial pressure and uterine artery pulsatility index. On top of each panel are the risk cut‐offs (i.e. 1 in…).

Figure 4

Calibration plots for estimated risk of delivery with pre‐eclampsia (PE) at (a) < 28 weeks, (b) < 32 weeks and (c) < 36 weeks' gestation in screening by maternal risk factors, estimated fetal weight and mean arterial pressure. Observed incidence is given as median with 95% CI (vertical solid lines). Numbers in red are the observed number of women who developed PE and numbers in black below are the total number of women within each estimated risk group. Diagonal line is line of perfect agreement. Overall mean risk is shown by vertical dashed line and overall incidence is shown by horizontal dashed line. Gray boxes represent unaffected pregnancies and red boxes represent pregnancies with PE. AUC, area under the curve.

Figure 5

Calibration plots for estimated risk of delivery with pre‐eclampsia (PE) at (a) < 28 weeks, (b) < 32 weeks and (c) < 36 weeks' gestation in screening by maternal risk factors, estimated fetal weight, mean arterial pressure and uterine artery pulsatility index. Observed incidence is given as median with 95% CI (vertical solid lines). Numbers in red are the observed number of women who developed PE and numbers in black below are the total number of women within each estimated risk group. Diagonal line is line of perfect agreement. Overall mean risk is shown by vertical dashed line and overall incidence is shown by horizontal dashed line. Gray boxes represent unaffected pregnancies and red boxes represent pregnancies with PE. AUC, area under the curve.