Fetal macrosomia, maternal obesity, prolonged second-stage labor, and a prior event raise risks for shoulder dystocia (Mehta, 2004; Overland, 2009; Schummers, 2015). Although these factors are clearly associated with this complication, identification of individual instances before the fact has proved to be impossible. The American College of Obstetricians and Gynecologists (2017 c) reviewed studies and concluded that: 1.
Most cases of shoulder dystocia cannot be accurately predicted or prevented.
2.
Elective induction of labor or elective cesarean delivery for all women suspected of having a macrosomic fetus is not appropriate.
3.
Planned cesarean delivery may be considered for the nondiabetic woman with a fetus whose estimated fetal weight is > 5000 g or for the diabetic woman whose fetus is estimated to weigh >4500 g.
There is a corresponding rise in the incidence of shoulder dystocia with increasing birthweight (Acker, 1985; 0verland, 2012; Stotland, 2004). Commonly cited maternal characteristics associated with increased fetal birthweight are obesity, postterm pregnancy, multiparity, and diabetes (Jolly, 2003; Koyanagi, 2013). The combination of fetal macrosomia and maternal diabetes mellitus escalates the frequency of shoulder dystocia (Langer, 1991; Nesbitt, 1998). This predisposition may stem from the fact that fetuses of diabetic women have larger shoulder and extremity circumferences and greater shoulder-to-head and chest-to-head size diferences relative to comparable-weight fetuses of nondiabetic mothers (McFarland, 1998; Modanlou, 1982). That said, translating these specific measurements into stand-alone sonographic clinical thresholds has shown poor predictive sensitivity (Burkhardt, 2014).
Preventively, early labor induction has yielded conflicting results. In one study, approximately 800 women with suspected macrosomic fetuses were randomized either to early induction between 37 and 39 weeks or to expectant care (Boulvain, 2015). Dystocia rates were lowered by two thirds in the intervention group, and neither group sufered brachial plexus injury. Although not measured, this practice is balanced against morbidity of early delivery. Moreover, the poor accuracy of antepartum fetal weight prediction should be considered as well (Hoopmann, 2010; Mlin, 2016; Noumi, 2005). In contrast, an earlier randomized study of 284 women showed that rates of shoulder dystocia were not lowered by early induction at 38 weeks (Gonen, 1997).
As previously discussed, cesarean delivery may be considered to prevent shoulder dystocia. hat said, Rouse and Owen (1999) concluded that a prophylactic cesarean delivery policy for macrosomic fetuses would require more than 1000 cesarean deliveries with attendant morbidity to avert a single permanent brachial plexus injury.
he risk of recurrent shoulder dystocia ranges from 1 to 13 percent (Bingham, 2010; Moore, 2008; Ouzounian, 2013). For many women with prior shoulder dystocia, a trial of labor may be reasonable. he American College of Obstetricians and Gynecologists (2017 c) recommends that estimated fetal weight, gestational age, maternal glucose intolerance, and severity of prior neonatal injury be evaluated and risks and benefits of cesarean delivery discussed with any woman with a history of
FIGURE 27-5 The McRoberts maneuver. The maneuver consists of removing the legs from the stirrups and sharply flexing the thighs up toward the abdomen. The assistant is also providing suprapubic pressure simultaneously (arrow).
shoulder dystocia. After discussion, either mode of delivery may be appropriate.