Use of Customized Birth Weight Percentiles for the Prediction of Shoulder Dystocia

Abstract

INTRODUCTION: To investigate the use of customized birth weight percentiles as a predictor for shoulder dystocia. METHODS: Over a 3-year period, shoulder dystocia occurred among 99 of 11,493 deliveries, for an incidence of 0.9%. To conduct a case–control study, 386 deliveries with no shoulder dystocia were randomly selected. Customized birth weight percentile was determined for each woman using Gestation Related Optimal Weight software, which accounts for maternal height, weight, ethnicity, parity, gestational age, and neonate sex. The relationship between customized birth weight percentile and shoulder dystocia was examined using logistic regression and receiver operating characteristic (ROC) curve analysis. RESULTS: The area under the ROC curve for customized birth weight percentile was 0.84 (95% confidence interval [CI] 0.80–0.88), indicating moderate performance of customized birth weight percentile as a risk discriminator. The 70th percentile had the highest sensitivity (79%) and specificity (76%) for prediction of shoulder dystocia (positive likelihood ratio 3.3, negative likelihood ratio 3.6). The area under the ROC curve for birth weight) alone was also 0.84 (95% CI 0.79–0.88). The average birth weight was 3,983 g (standard deviation 516) for those in the case group and 3,320 (standard deviation 435) for those in the control group (P<.001). Most cases of shoulder dystocia (85%) occurred at a birth weight of less than 4,500 g and only three (0.03%) would have been offered prophylactic cesarean delivery based on American College of Obstetricians and Gynecologists recommendations. CONCLUSIONS: Customized birth weight percentile is not an accurate predictor of shoulder dystocia and performs no better than birth weight alone. Continued efforts to identify patients at high risk for shoulder dystocia are needed among those with weights lower than that used to offer prophylactic cesarean delivery by American College of Obstetricians and Gynecologists recommendations.