First-trimester Placental Ultrasound (FirstPLUS) study: prediction of fetal growth restriction using OxNNet-derived first-trimester placental volume.

objectivesTo develop predictive models for fetal growth restriction (FGR) with and without the inclusion of OxNNet-derived first-trimester placental volume (FTPV), thereby evaluating the contribution of FTPV to these models and the extent to which FTPV percentile is associated with subsequent FGR.

methodsThis study utilized data from the First-trimester Placental Ultrasound (FirstPLUS) study, a longitudinal observational cohort study conducted at King's College Hospital NHS Foundation Trust, London, UK, between March and November 2022. Participants underwent routine ultrasound assessment between 11 + 2 and 14 + 1 weeks' gestation, in addition to three-dimensional placental sonography. The OxNNet toolkit was used for automated placental segmentation and volume calculation. Multivariable logistic regression models were developed to predict FGR, incorporating maternal factors, first-trimester biomarkers (serum pregnancy-associated plasma protein-A, mean arterial blood pressure and uterine artery pulsatility index) and FTPV.

resultsThe final cohort comprised 3500 pregnancies, of which 250 (7.1%) developed FGR. Low FTPV was found to be a risk factor for FGR, with an odds ratio of 1.736 (95% CI, 1.499-2.015) per unit decrease in FTPV Z-score. Incorporating FTPV into the predictive model based on maternal factors and biomarkers significantly increased the area under the receiver-operating-characteristics curve (AUC) for predicting all cases of FGR, from 0.78 (95% CI, 0.75-0.81) to 0.79 (95% CI, 0.76-0.82) (P = 0.005). Subgroup analysis of normotensive and hypertensive cases demonstrated a statistically significant effect size for the prediction of FGR by FTPV Z-score in both groups. The addition of FTPV to the model based on maternal factors and biomarkers for the prediction of normotensive FGR increased the AUC from 0.77 (95% CI, 0.74-0.80) to 0.78 (95% CI, 0.75-0.81) (P = 0.01). For preterm FGR, the AUC was 0.85 (95% CI, 0.78-0.92) with FTPV and 0.85 (95% CI, 0.79-0.92) without (P = 0.93); the absence of a significant difference may be due to a lack of power.

conclusionsFTPV Z-score is a predictor of FGR. Integrating FTPV into predictive models significantly enhanced the discriminative ability for all cases of FGR, as well as for the subgroup of normotensive FGR. © 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.