Risk factors and planning delivery of high-risk pregnancies

Vaginal delivery is complicated by shoulder dystocia when, after delivery of the fetal head, additional obstetric maneuvers beyond gentle guidance are needed to enable the delivery of the fetal shoulders. Shoulder dystocia is an obstetric emergency because it may result in life-threatening infant injuries, as well as less serious maternal injuries. It has been estimated that one newborn with hypoxic-ischemic encephalopathy due to shoulder dystocia is born in every 22,000 term vaginal births [1].

This topic will discuss antepartum issues related to shoulder dystocia: risk factors for the disorder and planning delivery when these risk factors are identified before labor. However, since many shoulder dystocias occur in pregnancies without risk factors, clinicians should always be prepared for the occurrence of the disorder. Intrapartum issues, including pathophysiology, diagnosis, management, and outcome of shoulder dystocia are reviewed separately. (See “Shoulder dystocia: Intrapartum diagnosis, management, and outcome”.)

CAN SHOULDER DYSTOCIA BE PREDICTED?

The occurrence of shoulder dystocia cannot be accurately predicted by antenatal or intrapartum risk factors or imaging studies [ 2]. (See ‘Risk factors’ below and ‘Pelvimetry and fetal biometry’ below.)

Nevertheless, clinicians should be aware of risk factors for shoulder dystocia in order to discuss possible scheduled cesarean delivery with women at highest risk of occurrence. Since at least 50 percent of pregnancies complicated by shoulder dystocia have no identifiable risk factors, the predictive value of any one or combination of risk factors for shoulder dystocia is low (less than 10 percent) [3-5]. Therefore, all obstetric care providers should be able to (1) promptly recognize when gentle traction alone is inadequate for delivery of the shoulders and (2) proceed through an orderly sequence of maneuvers to deliver the neonate in a timely manner, with no or minimal maternal and fetal trauma.

It should be noted, however, that permanent birth injury, and even perinatal death, can occur in cases of shoulder dystocia that are appropriately identified and managed. Furthermore, neonatal brachial plexus palsy can occur in infants delivered by cesarean [6].