This study compared the odds of adverse obstetrical outcomes of pregnancies in women who conceived from IVF (n=464) versus spontaneous conception (n=1171) after stratification into three body mass index (BMI) groups: normal weight (18.5–24.9 kg/m2), overweight (25.0–29.9 kg/m2) and obese (>30 kg/m2). With increasing BMI, incidences of complications between IVF and spontaneously conceived groups narrowed. Among women with normal BMI, IVF pregnancies were associated with increased odds of placental ischaemic disorders (11.3% versus 7.0%, adjusted odds ratio [aOR]=2.24; 95% confidence interval [CI]=1.25–4.04) and low birthweight <2500 g (10.6% versus 8.0%, aOR=2.08; 95% CI=1.12–3.88). Among overweight women, only low birthweight (<2500 g) was significantly increased (15.6% versus 6.2%, aOR=4.33; 95%, CI=1.61–11.63). For obese women, there were no differences between IVF and spontaneously conceived pregnancies for either placental ischaemic disorders (12.5 versus 20.2%, OR=0.43, 95% CI=0.17–1.1) or low birthweight (10.0% versus 11.0%, aOR=0.7, 95% CI=0.24–2.08). Overall, the odds of adverse obstetrical outcomes were not significantly greater in IVF singleton pregnancies compared with those conceived spontaneously as BMI increased.