Objective: The purpose of this study was to examine the 1-year incidence statewide in California of shoulder dystocia and its associated risk factors.
Study design: With a data set that contains computer-linked records from the birth certificate and hospital discharge records of both mother and baby, all births of infants >3500 g in >300 civilian acute care hospitals in California in 1992 were analyzed. All cases of shoulder dystocia were identified from discharge records, birth certificates, or both and were analyzed with both bivariate and multivariate techniques to identify specific risk factors.
Results: A total of 175,886 vaginal births of infants >3500 g were included in our database, of which 6238 infants (3%) had shoulder dystocia. The percentages of births complicated by shoulder dystocia for unassisted births not complicated by diabetes were 5.2% for infants 4000 to 4250 g, 9.1% for those 4250 to 4500 g, 14.3% for 4500 to 4750, and 21.1% for those 4750 to 5000 g. Shoulder dystocia increased by approximately 35% to 45% in vacuum- or forceps-assisted births to nondiabetic mothers. Similar increases were seen in unassisted births to diabetic mothers. The risk of shoulder dystocia for assisted births to diabetic mothers was even more dramatic: 12.2% for infants 4000 to 4250 g, 16.7% for those 4250 to 4500 g, 27.3% for those 4500 to 4750 g, and 34.8% for those 4750 to 5000 g. After controlling for other parameters, there was an increased risk of shoulder dystocia associated with diabetes (odds ratio 1.7), assisted delivery (odds ratio 1.9), and induction of labor (odds ratio 1.3). Rates of birth trauma, asphyxia, and length of stay were all increased among births complicated by shoulder dystocia.
Conclusion: This information on the incidence of shoulder dystocia and associated risk factors for a large statewide population may assist providers of obstetric care in counseling patients when macrosomia is suspected. The inaccuracy of estimating fetal weight is a severe limitation in attempting to establish guidelines designed to prevent shoulder dystocia.