Large-for-gestational-age neonates: anthropometric reasons for shoulder dystocia.

From 1960 to 1980 at Memorial Hospital Medical Center--Miller Children's Hospital, the mean birth weight for term-size neonates increased from 3381 to 3458 g inspite of increases in ethnic groups known to have smaller neonates. More significantly, the incidence of macrosomic neonates (birth weight greater than 4000 g) increased from 7.0 to 10.7%. Because of this marked increase in the incidence of neonatal macrosomia, prospective study was designed to characterize the macrosomic neonate anthropometrically. The results of this study revealed that neonates experiencing shoulder dystocia had significantly greater shoulder-to-head and chest-to-head disproportions than did macrosomic neonates delivered by cesarean section for failed progress in labor or macrosomic neonates delivered without shoulder dystocia. In addition, neonates of diabetic mothers also showed significantly greater shoulder-head and chest-head size differences than did neonates of nondiabetic mothers of comparable weight. These data suggest that antenatal ultrasonic measurements to compare chest-head size difference in fetuses suspected to be macrosomic and in diabetic pregnancies could be of value in selecting patients for the appropriate route of delivery.