Objective To assess the prevalence of overweight and obesity, and the impact of body mass index (BMI) on maternal and neonatal outcomes, in a UK obstetric population. ). Maternal and neonatal outcomes were examined using logistic regression, adjusted for confounding variables.Main outcome measures Maternal and neonatal outcomes.Results Compared with women of normal weight, women who were overweight or obese class I were at significantly increased risk of hypertensive disorders of pregnancy (OR 1.9, 99% CI 1.7-2.3; OR 3.5, 99% CI 2.9-4.2); gestational diabetes mellitus (OR 1.7, 99% CI 1.3-2.3; OR 3.7, 99% CI 2.8-5.0); induction of labour (OR 1.2, 99% CI 1.1-1.3; OR 1.3, 99% CI 1.2-1.5); caesarean section (OR 1.4, 99% CI 1.3-1.5; OR 1.8, 99% CI 1.6-2.0); postpartum haemorrhage (OR 1.4, 99% CI 1.3-1.5; OR 1.8, 1.6-2.0); and macrosomia (OR 1.5, 99% CI 1.3-1.6; OR 1.9, 99% CI 1.6-2.2), with the risks increasing for obese classes II and III. Women in obese class III were at increased risk of preterm delivery (OR 1.6, 99% CI 1.1-2.5), stillbirth (OR 3.0, 99% CI 1.0-9.3), postnatal stay > 5 days (OR 2.1, 99% CI 1.5-3.1), and infant requiring admission to a neonatal unit (OR 1.6, 99% CI 1.0-2.6).Conclusions By categorising women into overweight and obesity subclassifications (classes I -III), this study clearly demonstrates an increasing risk of adverse outcomes across BMI categories, with women who are overweight also at significant risk.

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