Pre-pregnancy body mass index (BMI) and macrosomia in a Canadian birth cohort

To compare demographic characteristics and maternal, fetal, neonatal, and pregnancy outcomes of term macrosomic infants of obese and non-obese mothers.

A sample of 1996 singleton, term deliveries was drawn from the All Our Babies Cohort, a prospective, community-based pregnancy cohort. Maternal self-reported socio-demographic and anthropometric information was linked to the clinical data on pregnancy and birth events abstracted from electronic health records. Demographic, obstetrical characteristics and maternal, fetal, neonatal, and pregnancy outcomes of macrosomic infants in obese, overweight, and normal weight women were compared. Multinomial regression analysis assessed the risk factors of macrosomia in primiparous and multiparous women stratified by maternal pre-pregnancy BMI, controlling for confounding variables.

Macrosomia affected 10% of pregnancies in the study. Mothers whose infants were macrosomic were more likely to be Caucasian, obese, have had previous deliveries, undergo induction of labour and delivery by emergency C-section, particularly for labour abnormalities. Macrosomic infants were more likely to be delivered postdates, have meconium stained liquor and require resuscitation at birth. There were no significant differences in birth and neonatal outcomes of macrosomic pregnancies between obese, overweight and normal weight women. Pre-pregnancy BMI and gestational age at delivery were risk factors for macrosomia in all women. Ethnicity and history of delivery of a macrosomic infant were additional independent risk factors in multiparas.

Obesity in pregnancy increases the risk of delivery of a macrosomic infant in both primiparous and multiparous women. The maternal, fetal and neonatal outcomes of macrosomic pregnancies are similar in obese and normal weight women.