Validation of the Fetal Medicine Foundation competing risks model for small for gestational age neonates in early third trimester

Abstract

ABSTRACTObjectivesTo evaluate the new 36 weeks’ Fetal Medicine Foundation (FMF) competing risks model for the prediction of small for gestational age (SGA) at an earlier gestation of 30+0 to 34+0 weeks.MethodsThis is a retrospective multi‐center cohort study of prospectively collected data on 3,012 women with singleton pregnancies undergoing ultrasound examination at 30+0 ‐ 34+0 weeks’ gestation, as part of a universal screening program. We used the default 36 weeks’ FMF competing risks model for prediction of SGA, combining maternal factors (age, obstetric and medical history, weight, height, smoking, race, conception), estimated fetal weight (EFW) and uterine artery pulsatility index (UtA‐PI), to calculate risks for different cut‐offs of birth weight percentile and gestational age at delivery. We examined the model's accuracy by means of discrimination and calibration.ResultsThe prediction of SGA<3rd percentile improves with the addition of UtA‐PI and with shorter examination‐to‐delivery interval. For 10% false positive rate, maternal factors, EFW and UtA‐PI predicted 88.0%, 74.4% and 72.8% of SGA <3rd percentile delivered <37, <40 and <42 weeks, respectively. The corresponding figures for SGA 10th percentile were 83.9%, 69.3% and 66.2%. In terms of population stratification, if the biomarkers used are EFW and UtA‐PI and the aim is to detect 90% of SGA <10thpercentile, then 10.8% of the population should be scanned within two weeks after the initial assessment, an additional 7.2% (total screen positive rate, SPR 18%) should be scanned within two and four weeks after the initial assessment and an additional 11.7% (total SPR 29.7%) should be examined within four and six weeks after the initial assessment. The new model was well calibrated.ConclusionsThe 36 weeks’ FMF competing risks model for SGA is also applicable and accurate at 30+0 ‐ 34+0 weeks’ gestation, providing effective risk stratification, especially for cases leading to birth <37 weeks.This article is protected by copyright. All rights reserved.