Introduction Overweight and obesity in pregnancy have adverse clinical implications for the mother. The prevalence of Caesarean section (CS) among the UK obstetric population has been increasing in recent years. This study investigated the association between body mass index (BMI) in early pregnancy and CS among singleton pregnancies in North East England.

Methods Data consist of all singleton pregnancies resulting in live birth or stillbirth and delivered at five maternity units in North East England between 1 January 2003 and 31 December 2005. BMI was obtained from electronic maternity records and was based on BMI recorded at booking. Logistic regression models were used to determine the adjusted odds ratios (aOR) of a CS among overweight (BMI 25–29.9 kg/m²) and obese (≥30 kg/m²) women, compared to those of recommended BMI (18.5–24.9 kg/m²)

Results There were 40 790 singleton pregnancies, of which 8392 (20.6%) were delivered by CS. Of those with recorded BMI, 16.4% were obese, 26.3% were overweight and 53.8% were of recommended BMI. 28.4% of obese and 21.9% of overweight pregnant women delivered by CS compared to 17.8% of women of recommended BMI. The adjusted odds ratio of CS (adjusted for maternal age, gestational age, birth weight, pregestational diabetes, ethnicity and index of multiple deprivation) was significantly increased among obese (OR 1.81 (95% CI 1.68 to 1.96; p<0.0005)) and overweight (OR 1.27 (95% CI 1.19 to 1.36; p<0.0005)) pregnant women, compared to women of recommended BMI.

Conclusion There is an almost twofold increased risk of delivery by CS among women who are obese.