Mode of delivery and outcomes by birth weight among spontaneous and induced singleton cephalic nulliparous labors

ObjectiveTo assess the effect of birth weight on mode of delivery among nulliparous women in a setting with no policy of elective induction for suspected macrosomia.MethodsIn an observational study, data were assessed from nulliparous women with a single cephalic pregnancy of at least 37 weeks in spontaneous (Robson group 1) and induced (Robson group 2a) labor attending a hospital in Dublin, Ireland, between January 1, 2008, and December 31, 2009. The primary outcome measure was mode of delivery.ResultsA total of 7528 nulliparous labors were included (4989 in group 1 and 2539 in group 2a). The cesarean section rate was 15.1% overall (n = 1139), with 411 (8.2%) in group 1, and 728 (28.7%) in group 2a. Cesarean delivery rates rose with increasing birth weight in group 1, from 119 (6.3%) of 1886 infants weighing 3000–3499 g and 160 (8.5%) of 1892 weighing 3500–3999 g, to 19 (26.8%) of 71 weighing 4500–4999 g. Rates of cesarean delivery were significantly higher in induced labor (group 2a) for each birth-weight category, ranging from 202 (25.9%) of 781 weighing 3000–3499 g and 243 (27.0%) of 899 weighing 3500–3999 g, to 38 (48.1%) of 79 weighing 4500–4999 g (P < 0.01 for all).ConclusionIn a setting with standardized management of labor, birth weight remains a significant determinant of mode of delivery.