2025/10/24 by M. Granfors, Ä. Mantel, O. Axelsson +2
paper · doi:10.1002/uog.70117
ABSTRACT Objective Ultrasound‐based fetal growth assessment is an essential part of clinical decision‐making in modern obstetric care. This study aimed to evaluate the impact of maternal and fetal characteristics on the accuracy and precision of sonographic fetal weight estimation. Methods We included 31 521 singleton pregnancies registered in the Swedish Pregnancy Register between January 2014 and December 2021, with delivery ≥ 22 + 0 weeks' gestation and estimated fetal weight (EFW) assessed using ultrasound within 2 days before delivery. Fetal biometric ultrasound measurements were used to calculate EFW according to the formula of Persson and Weldner. Mean percentage error (MPE) and the proportion of EFW within ± 10% of the birth weight were calculated and stratified by maternal body mass index (BMI), fetal sex, fetal presentation at birth, gestational age (GA) at ultrasound and standardized EFW (estimated small‐for‐gestational age (SGA), appropriate‐for‐gestational age (AGA) or large‐for‐gestational age). Univariable and adjusted risk ratios (aRRs) for poor EFW assessment, defined as EFW deviating more than ± 10% from the birth weight, were calculated. Results All investigated fetal characteristics, but not maternal BMI, affected the precision of EFW. The inaccuracies of fetal weight estimation were most pronounced in fetuses estimated as severe SGA ( rd percentile) across all subgroups of GA at ultrasound (overall MPE, −5.4 ± 9.8%; 67% of estimates within ± 10% of birth weight). The risk of poor fetal weight estimation was highest for severe‐SGA‐estimated vs AGA‐estimated fetuses (aRR, 1.44 (95% CI, 1.38–1.51)). Additionally, the risk of poor fetal weight estimation was higher for male vs female fetuses (aRR, 1.09 (95% CI, 1.05–1.14)), non‐cephalic vs cephalic presentation (aRR, 1.20 (95% CI, 1.13–1.28)) and preterm vs late term (39 + 0 to 40 + 6 weeks) GA at ultrasound, with the highest risk observed for those with GA of 22 + 0 to 27 + 6 weeks at ultrasound (aRR, 1.30 (95% CI, 1.13–1.50)). Conclusions All assessed fetal characteristics, especially standardized EFW, affected the accuracy of ultrasonographic fetal weight estimation. Understanding systematic errors in the EFW formula used is of utmost importance in clinical decision‐making to prevent unnecessary or missed obstetric interventions. © 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.