The effect of maternal obesity on the accuracy of fetal weight estimation

OBJECTIVE: To determine if maternal obesity affects the accuracy of either clinical or sonographic fetal weight estimations. METHODS: In a year-long study, 998 singleton pregnancies of 26-43 weeks' gestation underwent both clinical (Leopold) and sonographic (Shepard and Hadlock) fetal weight estimation within 5 days of delivery (mean 1.1, 95% confidence interval 1.0-1.3). Patients were stratified into four different groups based on increasing maternal body mass index (BMI): underweight (less than 19.8), normal weight (19.8-26.0), overweight (26.1-29.0), and obese (more than 29.0). The various estimations of fetal weight were compared with actual birth weight, and the mean absolute percent error was calculated for each specific method and analyzed among the four BMI groups. RESULTS: For each method of weight estimation, there was no difference (specifically, no increase) in the magnitude of the absolute percent error with increasing maternal obesity. Regardless of maternal size, almost half of the weight predictions were within 5% of the actual birth weight. CONCLUSION: Increasing maternal obesity does not alter or decrease the accuracy of either clinical or sonographic fetal weight estimations. Therefore, fetal weight predictions provide equally accurate and valid guidelines for determining management decisions in women, regardless of body size.