Induction of Labor for Suspected Fetal Macrosomia Between 37 Weeks and 38 6/7 Weeks Gestational Age May Reduce Shoulder Dystocia

EBM Focus - Volume 10, Issue 26

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Reference - Lancet 2015 June 27;385(9987):2600 (level 2 [mid-level] evidence)

Fetal macrosomia and large for gestational age status are associated with an increased risk of neonatal and maternal complications including shoulder dystocia and emergency cesarean section (Aust N Z J Obstet Gynaecol 2009 Oct;49(5):504). Prophylactic cesarean delivery and early term induction of labor have each been suggested to prevent delivery complications and continued fetal growth. Neither strategy, however, is recommended for routine use in pregnant women with suspected fetal macrosomia (Obstet Gynecol. 2002 Nov;100(5 Pt 1):1045, RCOG 2012 Mar PDF). A previous Cochrane review of 3 randomized trials found no significant reduction in the risk of shoulder dystocia with labor induction. However this result is limited by most included women being at ≥ 40 weeks gestation and the small number of trials found (Cochrane Database Syst Rev 2000;(2):CD000938). A recent randomized trial compared labor induction vs. expectant management in 822 pregnant women with singleton fetus at gestational age of 36-38 weeks with estimated weight > 95th percentile for gestation age. Induction occurred within 3 days of randomization at gestational age between 37 weeks and 38 6/7 weeks.

The primary outcome was a composite of significant shoulder dystocia, clavicle or long bone fractures, brachial plexus injury, intracranial hemorrhage, or death. Significant shoulder dystocia was defined as difficulty delivering the shoulders not resolved by McRoberts maneuver, usually combined with suprapubic pressure, or births with > 60 second interval between delivery of head and body. Overall, induction of labor occurred in 89% of women randomized to induction vs. 28% in the expectant management group. The primary composite outcome occurred in 2% of neonates with labor induction vs. 6% with expectant management (p = 0.004, NNT 25). In analyses of individual outcomes, labor induction was associated with a reduction in significant shoulder dystocia (1% vs. 4%, p < 0.05, NNT 34) as well as any shoulder dystocia (4% vs. 8%, p < 0.05, NNT 25). In addition, one concern with labor induction is the risk of increasing cesarean section rates, but in this trial, induction was associated with an increase in spontaneous vaginal delivery (59% vs. 52%, p < 0.05, NNT 15) and no significant differences in rates of cesarean section or assisted vaginal delivery. There were no significant differences in other maternal adverse outcomes or in rates of neonatal fractures and no cases of brachial plexus injury, intracranial hemorrhage, or neonatal death.

The trial was terminated early due to slow recruitment after enrolling 822 women, with the original plan calling for 1,000 women. Nonetheless, this trial was still much larger than previous trials evaluating labor induction for fetal macrosomia and was therefore better powered to detect differences in outcomes presenting in a small percentage of newborns. Most of the trials in the previous Cochrane review were small, with only 372 births and 18 cases of shoulder dystocia in the 3 trials combined (Cochrane Database Syst Rev 2000;(2):CD000938). In this trial, other neonatal adverse outcomes, including admission to the neonatal intensive care unit and hyperbilirubinaemia, were similar between groups, suggesting labor induction did not increase the risk of morbidity to either mother or child. It is worth noting, however, that previous studies have found increased morbidity in a large cohort of infants delivered electively at 37-39 weeks, although there was no subgroup analysis of infants who were large for gestational age. Overall, the new results suggest that induction of labor may be a preferred option in early term neonates with suspected macrosomia.

For more information, see the Shoulder dystocia topic in DynaMed.