Shoulder dystocia and brachial plexus injury: a case-control study

Objective and Background. To evaluate risk factors for shoulder dystocia and brachial plexus injury using a case-control study at the departments of obstetrics and gynecology at the four largest hospitals in southern Sweden. All cases of shoulder dystocia between 1987 and 1993 inclusive were identified. For each case, two control infants with similar birthweight (+/- 100 g) and identical year of birth were randomly selected. Methods. Original maternal records were reviewed and information regarding 10 potential risk factors was extracted. Odds ratios (ORs) were calculated using the Mantel-Haenszel method. Stratification was made for year of delivery, parity (0, I, II, III+), and maternal age (5-year class). Results. In all, 107 infants with shoulder dystocia and 198 controls were included. The OR was greater than unity for all risk factors except gestational age. Three of the risk factors, induction of labor, epidural analgesia, and instrumental delivery, reached statistical significance. Thirty-four infants also suffered brachial plexus injury, giving a brachial plexus injury rate of 32% among the shoulder dystocia cases. We also made a separate analysis of the nine risk factors for brachial plexus injury following a shoulder dystocia, however none reached statistical significance. Conclusion. In this case-control study based on more than 100 000 deliveries at four large hospitals during a 7-year period, induction of labor, epidural analgesia, and instrumental delivery turned out to be significant risk factors for shoulder dystocia. For brachial plexus injury following shoulder dystocia, no significant risk factor was identified.