Abstract

Objectives: To evaluate the effect of aspirin on gestational age at delivery due to preterm pre-eclampsia (PE) in women with chronic hypertension (CH), to assess the predictive performance of the Fetal Medicine Foundation (FMF) first-trimester competing-risks model for preterm PE in this high-risk group and to evaluate how parity, previous PE and biomarker values influence individualized risk estimates.

Methods: We analyzed data from two multicenter first-trimester PE screening studies: the Combined Multimarker Screening and Randomized Patient Treatment with Aspirin for Evidence-based Preeclampsia Prevention trial and the Screening Program for Preeclampsia trial. The effect of aspirin on gestational age at delivery due to PE was assessed using Bayesian inference. The screening performance of the FMF model was evaluated by discrimination, calibration and decision-curve analysis. The influence of parity, previous PE and biomarkers (mean arterial pressure (MAP), uterine artery pulsatility index (UtA-PI) and placental growth factor (PlGF)) on risk classification was explored using empirical data and Monte Carlo simulations with generalized additive models.

Results: The combined dataset included 51 024 women with a singleton pregnancy, of whom 556 (1.1%) had CH. Among the women with CH, 58 (10.4%) developed preterm PE. Bayesian analysis indicated that aspirin delayed delivery due to PE by a mean of 3.6 (95% credible interval, 0.2-6.6) weeks, with a 98% posterior probability of benefit. The FMF model demonstrated good discrimination (area under the receiver-operating-characteristics curve, 0.819 (95% CI, 0.763-0.874)), adequate calibration and higher net benefit compared with a treat-all approach. Overall, 21.8% of women with CH were classified as low risk (< 1 in 100) for preterm PE, consisting mostly of nulliparous women and parous women without previous PE. Predicted risks for preterm PE were strongly influenced by MAP and PlGF, with UtA-PI contributing to a lesser extent.

Conclusions: In women with CH, aspirin can delay delivery due to preterm PE, and first-trimester risk assessment using the FMF competing-risks model reliably identifies low- and high-risk individuals. The predicted risk is driven primarily by MAP and PlGF, supporting risk stratification and individualized management in early pregnancy. © 2026 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.