The effect of mode of conception on obstetrical outcomes differs by body mass index.

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/m(2)), overweight (25.0-29.9 kg/m(2)) and obese (>30 kg/m(2)). 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.