Objective  To investigate the risk factors, labor characteristics, and perinatal outcomes of shoulder dystocia (SD).

  Methods  The clinical data of 81 SD cases who were admitted to Peking Union Medical College from January 1993 to December 2012 were retrospectively analyzed. Meanwhile, 6299 cases of term vaginal deliveries of singleton offspring in cephalic presentation during the same period were enrolled as the control group. The risk factors of SD and its influence on the maternal and neonatal outcomes were retrospectively analyzed.

  Results  The incidence of SD during this period was 0.47% (81/17 287). The incidence of SD significantly increased in fetuses with gestational age of greater than 40 weeks and in mothers with diabetes mellitus (both P < 0.001). The SD group had significantly higher rates of uterine inertia (54.3%), abnormal fetal heart rate (27.2%), and meconium stained amniotic fluid (22.2%) than in the control group (all P < 0.001). More patients in the SD group received assisted deliveries (24.7%) and episiotomy (93.8%) (both P < 0.001). Newborns delivered after SD had significantly higher rates of asphyxia (19.8%), clavicular fracture (18.5%) and brachial plexus injury (6.2%) (all P < 0.001). Their body weight was also significantly higher (P=0.004). Multivariable analysis showed the independent risk factors for SD included macrosomia (OR=12.7; 95% CI:7.6-21.4), uterine inertia (OR=12.1; 95% CI:7.3-20.1), diabetes mellitus (OR=8.4; 95% CI:5.0-14.8), assisted deliveries (OR=6.6; 95% CI:3.5-12.4) and deliveries after due date (OR=2.6; 95% CI:1.6-4.3) (all P < 0.001).

  Conclusions  Macrosomia, deliveries after due date, and diabetes mellitus are risk factors of SD. SD should be suspected when secondary uterine inertia exists or assisted delivery is applied. The maternal and neonatal complications are closely related with fetal weight and assisted deliveries.