Buy Article Permissions and Reprints Abstract

Objective Error in birthweight prediction by sonographic estimated fetal weight (EFW) has clinical implications, such as avoidable cesarean or misclassification of fetal risk in labor. We aimed to evaluate optimal timing of ultrasound and which fetal measurements contribute to error in fetal ultrasound estimations of birth size at the extremes of birthweight.

Study Design We compared differences in head circumference (HC), abdominal circumference (AC), femur length, and EFW between ultrasound and corresponding birth measurements within 14 (n = 1,290) and 7 (n = 617) days of birth for small- (SGA, <10th percentile), appropriate- (AGA, 10th–90th), and large-for-gestational age (LGA, >90th) newborns.

Results Average differences between EFW and birthweight for SGA neonates were: −40.2 g (confidence interval [CI]: −82.1, 1.6) at 14 days versus 13.6 g (CI: −52.4, 79.7) at 7 days; for AGA, −122.4 g (−139.6, −105.1) at 14 days versus −27.2 g (−50.4, −4.0) at 7 days; and for LGA, −242.8 g (−306.5, −179.1) at 14 days versus −72.1 g (−152.0, 7.9) at 7 days. Differences between fetal and neonatal HC were larger at 14 versus 7 days, and similar to patterns for EFW and birthweight, differences were the largest for LGA at both intervals. In contrast, differences between fetal and neonatal AC were larger at 7 versus 14 days, suggesting larger error in AC estimation closer to birth.

Conclusion Using a standardized ultrasound protocol, SGA neonates had ultrasound measurements closer to actual birth measurements compared with AGA or LGA neonates. LGA neonates had the largest differences between fetal and neonatal size, with measurements 14 days from delivery showing 3- to 4-fold greater differences from birthweight. Differences in EFW and birthweight may not be explained by a single fetal measurement; whether estimation may be improved by incorporation of other knowable factors should be evaluated in future research.

Key Points

Ultrasound measurements may be inadequate to predict neonatal size at birth.

Birthweight estimation error is higher for neonates >90th percentile.

There is higher error in AC closer to birth.

Keywords anthropometry - biometry - birthweight infant - small-for-gestational age - large-for-gestational age Publication History

Received: 26 December 2023

Accepted: 24 March 2024

Accepted Manuscript online:
03 April 2024

Article published online:
10 May 2024

© 2024. Thieme. All rights reserved.

Thieme Medical Publishers, Inc.
333 Seventh Avenue, 18th Floor, New York, NY 10001, USA