Maternal body mass index and risk of obstetric, maternal, and neonatal outcomes: A cohort study of nulliparous women with spontaneous onset of labor

Introduction: This study investigates associations between maternal body mass index (BMI) early in pregnancy and obstetric interventions, maternal and neonatal outcomes. Material and methods: This is a cohort study of nulliparous women originally included in a cluster randomized controlled trial carried out at 14 Norwegian obstetric units between 2014 and 2017. The sample included 7189 nulliparous women with a singleton fetus, cephalic presentation and spontaneous onset of labor at term, denoted as group 1 in the Ten-Group Classification System. The women were grouped according to the World Health Organization's BMI classifications: underweight (BMI