A scoring system for detection of macrosomia and prediction of shoulder dystocia: A disappointment

Objective. To develop a scoring system for the detection of a macrosomic fetus (birth weight (BW) >= 4000 g) and predict shoulder dystocia among large for gestational age fetuses. Study design. We retrospectively identified all singletons with accurate gestational age (GA) that were large for GA (abdominal circumference (AC) or estimated fetal weight (EFW) >= 90% for GA) at >= 37 weeks with delivery within three weeks. The scoring system was: 2 points for biparietal diameter, head circumference, AC, or femur length >= 90% for GA, or if the amniotic fluid index (AFI) was >= 24 cm; for biometric parameters < 90% or with AFI 524 cm, 0 points. The predictive values for detection of shoulder dystocia were calculated. Results. Of the 225 cohorts that met the inclusion criteria the rate of macrosomia was 39% and among vaginal deliveries (n = 120) shoulder dystocia occurred in 12% (15/120; 95% confidence interval (CI) 7-20%). The sensitivity of EFW >= 4500 g to identify a newborn with shoulder dystocia was 0% ( 95% CI 0-21%), positive predictive values 0% ( 95% CI 0-46%), and likelihood ratio of 0. For a macrosomia score 46, the corresponding values were 20% (4-48%), 25% (5-57%) and 2.3. Conclusion. Though the scoring system can identify macrosomia, it offers no advantage over EFW. The scoring system and EFW are poor predictors of shoulder dystocia.