Growth in utero and body mass index at age 5 years in children of smoking and non-smoking mothers

Abstract

Background High birth weight is associated with overweight later in life, while tobacco exposure in utero is associated with low birth weight, but with later risk of overweight. Aims To examine whether body mass index (BMI) z-scores of children at age 5 are associated with measurements of mid-abdominal diameter (MAD) in utero comparing smoking and non-smoking mothers. Study Design Growth in utero was recorded as MAD in mm per days of gestational age (MAD for gestational age) at 17, 25, 33 and 37 weeks of gestation in 561 infants whose mothers participated in a population-based study in Scandinavia (1986–1988). Outcome Measures The offspring's BMI z-score at 5 years was used as a dependent variable, and MAD for gestational age as well as birth weight divided by gestational age in days were included as explanatory variables in separate linear regression models. Maternal BMI was considered as a potential confounder. Results At 17 and 25 weeks gestation there were no relevant differences in MAD for gestational age between smokers and non-smokers. At 33 and 37 weeks gestation, children of smoking mothers had less increase in MAD than children of non-smoking mothers. In adjusted models, MAD for gestational age in week 33 and 37 was positively associated with BMI z-score at 5 years of age among children of both smoking and non-smoking mothers. Conclusions In this study overweight in children exposed to tobacco smoking in utero was apparently not mediated through foetal growth retardation, followed by enhanced fat accretion after birth.