['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.', "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.", '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.'] Does delivery of the posterior arm reduce shoulder dimensions in shoulder dystocia?