En cas de macrosomie fœtale, la meilleure stratégie est le déclenchement artificiel du travail à 38 semaines d'aménorrhée

Macrosomic fetuses are at increased risk of obstetric complications, and notably shoulder dystocia, responsible for a severe neonatal morbidity. In case of fetal macrosomia, three options are: (i) the elective cesarean delivery, but this is recommended only when the estimated fetal weight is ≥ 4500 g for diabetic women and 5000 g for non-diabetic women; (ii) the expectative management, but children with birth weight ≥ 4500 had significantly increased risk of perinatal mortality, neonatal asphyxia, trauma, and cesarean delivery; (iii) the induction of labor which, reducing the possibility of fetal growth, reduce the risk of cesarean delivery for cephalopelvic disproportion and shoulder dystocia. As 2 former trials did not show maternal or neonatal benefit with induction of labor for fetal macrosomia, it was therefore not recommended. However, these 2 studies had small sample size (273 and 40 women) and a methodology limiting their ability to show a difference, justifying to achieve a large multicentre randomized controlled trial. This trial was performed by Boulvain et al. and the results published in 2015 in the Lancet. Inclusion criteria were: a singleton pregnancy in cephalic presentation and a suspected fetal macrosomia defined by an ultrasound estimated weight > 95th percentile between 36 and 38 weeks. Women were randomly assigned to receive induction of labor within 3 days between 37+0 and 38+6 weeks of gestation, or expectant management. Expectant management continued until either spontaneous labour or diagnosis of a condition necessitating induction. The primary outcome was a composite of clinically significant shoulder dystocia, fracture of the clavicle, brachial plexus injury, intracranial haemorrhage, or death. Baseline characteristics were similar between groups. The mean birth weight (± SD) was 3831 (± 324) g in the induction group 4118 (± 392) g in the expectant group. Induction of labor significantly reduced the risk of shoulder dystocia or associated morbidity (8/407; 2 %) compared with expectant management (25/411; 6 %); P = 0.004. The number needed to treat was 25 (95 % CI: 15-70). The incidence of caesarean section and operative vaginal delivery did not differ significantly between the groups. The likelihood of spontaneous vaginal delivery increased significantly in the induction of labor group (59 % vs. 52 %, RR: 1.14; 95 % CI: 1.01-1.29). In all, the results of the Boulvain et al. trial justify to propose an induction of labor in cases of suspected macrosomia > 95th percentile: the induction of labor reduced the risk of severe shoulder dystocia, and does not increase the risk of cesarean section. It even increases the likelihood of spontaneous vaginal delivery.