Fetal environment and subsequent obesity: a study of maternal smoking.

BACKGROUND The intrauterine environment may influence the development of obesity, but as yet, the long-term effect of growth in utero is unclear. We studied maternal smoking during pregnancy to gain insight on how an insult affecting fetal growth might subsequently influence obesity risk through childhood to age 33. METHODS Data from the 1958 British birth cohort (all births in England, Wales and Scotland, 3-9 March 1958), including body mass index (BMI), maternal smoking during pregnancy and several potential confounding factors. We assessed obesity risk at ages 7, 11, 16, 23 and 33 associated with maternal smoking. Adjusted odds ratios (OR) for obesity at age 33 were estimated for 2918 men and 2921 women with complete data. RESULTS Infants of mothers who smoked in pregnancy were lighter at birth than infants of non-smokers, but from adolescence (age 11 for females, 16 for males) they had an increased risk of being in the fattest decile of BMI. The OR for obesity associated with maternal smoking increased with age, suggesting strengthening of the relationship over time. At age 33 the OR was 1.56 (95% CI : 1.22-2.00) for men and 1.41 (95% CI : 1.12-1.79) for women. This was robust to adjustment for factors in early life, childhood and adulthood. CONCLUSIONS An elevated risk of obesity among the offspring of smokers was not accounted for by other known influences. Findings are consistent with a long-term effect of intrauterine environment on adiposity, possibly through fetal nutrition, although other mechanisms should be investigated in future studies of obesity.