For exigent delivery, forceps or vacuum device can be applied to a persistent OP position. This is often performed in conjunction with an episiotomy. Also, if the head is engaged, the cervix fully dilated, and the pelvis adequate, forceps rotation may be attempted for those with suitable skills. These operative vaginal techniques are detailed in Chapter 29 (p. 561).
Infrequently, protrusion of fetal scalp through the introitus is the consequence of marked elongation of the fetal head from molding combined with formation of a large caput succedaneum. In some cases, the head may not even be engaged-that is, the biparietal diameter may not have passed through the pelvic inlet. In these, labor is characteristically long and descent of the head is slow. Careful palpation above the symphysis may disclose the fetal head to be above the pelvic inlet. Prompt cesarean delivery is appropriate.
At Parkland Hospital, spontaneous delivery or manual rotation is preferred for management of persistent OP position. When needed, either manual rotation to OA position followed by forceps delivery or forceps delivery from the OP position is used. If neither can be completed with ease and safety, cesarean delivery is performed.
Following complete emergence of the fetal head during vaginal delivery, the remainder of the body may not rapidly follow. The anterior fetal shoulder can become wedged behind the symphysis pubis and fail to deliver using normally exerted downward traction and maternal pushing. Because the umbilical cord is compressed within the birth canal, this dystocia is an emergency. Several maneuvers, in addition to downward traction on the fetal head and neck, may be performed to free the shoulder. This requires a team approach, in which efective communication and leadership are critical.
Consensus regarding a speciic definition of shoulder dystocia is lacking. Some focus on whether maneuvers to free the shoulder are needed, whereas others use the head-to-body delivery time interval as deining (Beall, 1998). Spong and coworkers (1995) reported that the mean head-to-body delivery time in normal births was 24 seconds compared with 79 seconds in those with shoulder dystocia. These investigators proposed that a head-to-body delivery time >60 seconds be used to define shoulder dystocia. Currently, however, the diagnosis continues to rely on the clinical perception that the normal downward traction needed for fetal shoulder delivery is inefective.
Because of these difering deinitions, the incidence of shoulder dystocia varies. One recent review cites a clinically useful average of 1 percent of all deliveries (Ouzounian, 2016). The incidence has increased in recent decades, likely due to increasing fetal birthweight (MacKenzie, 2007; 0verland, 2014). Increased identiication and documentation may also raise the incidence (Kim, 2016).
In general, shoulder dystocia poses greater risk to the fetus than to the mother. The main maternal risks are serious perineal tears and postpartum hemorrhage, usually from uterine atony but also from lacerations (Gauthaman, 2016; Rahman, 2009). In contrast, significant neonatal neuromusculoskeletal injury and asphyxia are concerns. These specific injuries are described in Chapter 33 (p. 630). In one review of 1177 shoulder dystocia cases, brachial plexus injury was diagnosed in 11 percent and clavicular or humeral fracture in 2 percent (Chauhan, 2014). MacKenzie and associates (2007) reviewed 514 cases. Of the neonates, 7 percent showed evidence of acidosis at delivery, and 1.5 percent required cardiac resuscitation or developed hypoxic ischemic encephalopathy (HIE). In another review of 200 cases, rates of severe fetal acidosis and HIE were each 0.5 percent if delivery was completed within 5 minutes. These rates rose to 6 and 24 percent, respectively, with delivery delays �5 minutes (Leung, 2011a).