Delivery of the posterior arm reduces shoulder dimensions in shoulder dystocia.

OBJECTIVE: To evaluate a possible reduction in shoulder diameter and circumference by extending the posterior arm during delivery, for an easier birth in cases of shoulder dystocia. METHODS: In this study of 33 neonates the bisacromial diameter and axilloacromial circumference were measured within 72 h of birth, first with the neonate's arms by its chest and then with 1 arm extended above its head. Reductions in diameter and circumference were evaluated. RESULTS: The mean +/- SD differences in bisacromial diameter and axilloacromial circumference were 1.9 +/- 0.69 cm and 2.52 +/- 1.18 cm, respectively. A greater reduction was observed in neonates with a greater shoulder diameter. CONCLUSION: In cases of shoulder dystocia, delivery of the posterior arm should significantly reduce shoulder dimensions, especially in larger fetuses, and prevent a need for excessive traction.