4Tsur A, Sergienko R, Wiznitzer A, et al. Critical analysis of risk factors for shoulder dystocia [ J]. Arch Gynecol Obstet,2012,285 : 1225 - 1229.
5Overland EA, Vatten LJ, Eskild A. Risk of shoulder dystocia: associ- ations with parity and offspring birthweight. A population study of 1 914 544 deliveries[J]. Acta Obstet Gynecol Scand,2012,91 : 483 - 488.