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Estimated Fetal Weight Extrapolated from Recent Ultrasound as a Predictor of Birth Weight at Term

Resident: Anna McQuary, MD

Faculty Advisor: Marvin Williams, DO


Having an estimation of fetal weight at the time of birth is an important part of the delivery admission process. Infants who are born large for gestational age or small for gestational age have increased morbidity. Estimated fetal weight has been shown to predict LGA and SGA infants. There are several methods to predict estimated fetal weight at time of delivery including maternal estimation, clinician estimation, or ultrasonography. At OU, we routinely use a formula of 30 g/day fetal weight gain to calculate estimated fetal weight if the patient has had an ultrasound performed within the past four weeks. This formula is derived from Williams fetal growth curves, which was published in 1982. While there have been other studies validating fetal growth curves as predictors of birth weight, this formula of 30 g/day has not been validated. Therefore, the purpose of this study is to validate this method of calculating estimated fetal weight at the time of delivery.


This study is a retrospective chart review of women who were delivered at term at the OU and who received a growth ultrasound in the late third trimester, defined as 34w0d to 36w6d. The charts of 1070 women who delivered from the years 2019-2021 were included for analysis. The estimated fetal weight at the time of delivery was calculated using the formula of 30 g/day of fetal growth from the time of their recent ultrasound and this mean was compared to the mean birth weight. The primary outcome is mean difference between these values. Secondary outcomes include the sensitivity/specificity of detecting small for gestational age infants and large for gestational age infants. Several subgroups were additionally analyzed such as patients with morbid obesity, diabetes, ethnicity, advanced maternal age > 40 years old, and fetal growth restriction. Our exclusion criteria includes patients with poor dating, fetal anomalies, and multiple gestations.


Data analysis is currently ongoing. Final results/conclusions will be available in May.


Data analysis is currently ongoing. Final results/conclusions will be available in May.

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