1046: Accuracy of estimated fetal weight assessment in fetuses with congenital diaphragmatic hernia

Abstract

Estimated fetal weight (EFW) is determined by a formula that includes measurement of the fetal abdominal circumference. There is an accepted range of error of up to 20% in either direction for accuracy of EFW. The degree of error is potentially higher in fetuses with congenital diaphragmatic hernia (CDH), in which the abdominal contents are displaced into the fetal thorax, which may affect measurement of the abdominal circumference. There is no universally accepted method for assessing EFW in fetuses with CDH, and there are mixed results in the literature reporting on accuracy of EFW in these cases. This study aims to assess the accuracy of standard EFW assessment in fetuses with CDH. We hypothesize that standard EFW assessment will underestimate the EFW of fetuses with CDH due to decreased fetal abdominal circumference measurement. This is a retrospective cohort of fetuses diagnosed with CDH at a single center from 2012 to 2018. We excluded fetuses with multiple anomalies or confirmed chromosome abnormalities. EFW was calculated using the Hadlock formula with standard measurements of the fetal head, abdominal circumference, and femur length. To account for time interval between final growth ultrasound and birth, we used published estimates of fetal growth rate to establish a “projected” EFW. The percent difference between the projected EFW and actual birthweight was compared using the Wilcoxon Signed-Rank test. Complete data were available for 77 fetuses with CDH. The majority of fetuses (n=59, 76.6%) had left-sided CDH. The median [IQR] projected EFW was similar to the median birthweight at 3177g [2691-3568] and 3180g [2630- 3500], respectively. The median percent difference between projected birthweight and actual birthweight was 6.34% [3.21-11.83]. We found that the EFW was underestimated in a minority of cases (n=43, 44.2%). The median maternal BMI in our population was 31.4kg/m2 [25.2-37.1]. The median gestational age at delivery was 38w4d [37w1d-39w1d], with a median 13 [7-20] days between final EFW and delivery. In fetuses with CDH, standard measurements for fetal EFW show accuracy that is at least comparable to previously established margins of error for ultrasound assessment of fetal weight. Standard EFW assessment remains an appropriate method of estimating fetal weight in fetuses with CDH.