Shoulder dystocia occurs when, after delivery of the fetal head, the baby's anterior shoulder gets stuck behind the mother's pubic bone. If this happens, the remainder of the baby does not follow the head easily out of the vagina as it usually does during vaginal deliveries.

This simple definition of shoulder dystocia, however, glosses over many complexities. For example, should a delivery be categorized as involving shoulder dystocia only when there is some time delay -- 60 seconds is often suggested in this context-between the delivery of a baby's head and shoulders? Or is shoulder dystocia present any time that a delivering physician finds that the shoulders cannot be delivered with the normal amount of downward traction on the fetal head? Some have suggested that the definition of true shoulder dystocia requires that an obstetrician had to perform special maneuvers in order to deliver the shoulders.

Exactly how shoulder dystocia is defined is more than just a semantic issue. It sets the parameters for the collection of statistics related to shoulder dystocia, a necessity for research aimed at decreasing shoulder dystocia related injuries. It also determines when a baby's injuries might be attributed to a physician's actions during labor and delivery.