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

Background: Congenital diaphragmatic hernia is a congenital anomaly in which fetal abdominal organs herniate into the thoracic cavity through a diaphragmatic defect, which can impede fetal lung development. Standard formulas for estimated fetal weight include measurement of fetal abdominal circumference, which may be inaccurate in fetuses with congenital diaphragmatic hernia because of displacement of abdominal contents into the thorax.

Objectives: This study aimed to assess the accuracy of standard estimated fetal weight assessment in fetuses with congenital diaphragmatic hernia by comparing prenatal assessment of fetal weight with actual birthweight.

Study design: A retrospective cohort study of fetuses diagnosed with congenital diaphragmatic hernia was performed at a single center from 2012 to 2018. Fetuses with multiple anomalies or confirmed chromosome abnormalities were excluded. Estimated fetal weight was calculated using the Hadlock formula. Published estimates of fetal growth rate were used to establish a projected estimated fetal weight at birth from the final growth ultrasound, and the percentage difference between projected estimated fetal weight at birth and actual birthweight was calculated. A Wilcoxan rank-sum test was used to examine the difference between projected estimated fetal weight and birthweight.

Results: We had complete data for 77 fetuses with congenital diaphragmatic hernia. The majority (76.6%, 55 of 77) had left-sided congenital diaphragmatic hernia. The median [interquartile range] projected estimated fetal weight was similar to median birthweight, at 3177 g [2691-3568] and 3180 g [2630-3500], respectively, which did not represent a statistically significant difference between projected estimated fetal weight and birthweight (P = .66). The median absolute percentage difference between projected birthweight and actual birthweight was 6.3% [3.2-7.0]. Estimated fetal weight was overall underestimated in a minority of cases (44.2%, 34 of 77).

Conclusion: In fetuses with a congenital diaphragmatic hernia, standard measurements of fetal estimated fetal weight show accuracy that is at least comparable with previously established margins of error for ultrasound assessment of fetal weight. Standard estimated fetal weight assessment remains an appropriate method of estimating fetal weight in fetuses with congenital diaphragmatic hernia.