Accuracy of sonography to predict estimated weight in fetuses with gastroschisis

The purpose of this study was to determine whether sonographic formulas for estimating fetal weight are as accurate for fetuses affected with gastroschisis as they are for healthy fetuses. We hypothesized that because the most commonly used Hadlock formulas rely on the abdominal circumference as a biometric variable, estimates of birth weight are less reliable in fetuses with gastroschisis than in healthy fetuses.

We performed a chart review of all fetuses with a prenatal diagnosis of gastroschisis at 3 tertiary care institutions from 1990 to 2008. Charts were reviewed for clinical and sonographic data. The estimated fetal weight at the prenatal sonogram closest to delivery was compared to the birth weight. Published Hadlock formulas using 4 biometric parameters were used to calculate the estimated fetal weight. Data analysis was performed using the Student t test and χ(2) test for continuous and categorical variables, respectively.

One hundred eleven patients with gastroschisis were identified. Sixty-six patients had a prenatal sonogram with a calculated estimated fetal weight within 7 days of delivery; 88 patients had a sonogram within 14 days. The mean birth weights ± SD were 2292 ± 559 and 2477 ± 531 g in the 0- to 7- and 8- to 14-day groups, respectively. Sonographic biometric measurements underestimated the birth weight by an average of 5.6%. Intrauterine growth restriction was predicted in 72% of all pregnancies but was only present in 52%.

Our study shows a systematic error of birth weight underestimation when using the Hadlock formulas in fetuses affected with gastroschisis.