Weight growth in infants born to mothers who smoked during pregnancy

Objective - To determine whether maternal smoking during pregnancy causes impairment in growth after birth. Design - Longitudinal study. Setting - Six medical university centres of six towns of north, central, and south Italy, Subjects - 12 987 babies (10 238 born from nonsmoking mothers, 2276 from mothers smoking one to nine cigarettes a day, and 473 from mothers smoking ≥ 10 cigarettes a day) entered the study. Main outcome measures - Difference in weight gain between children born to smoking mothers and those born to non-smoking mothers. Weight was measured at birth and at 3 and 6 months of age. Maternal smoking habit was derived from interview on third or fourth day after delivery. Results - Compared with children born to mothers who did not smoke during pregnancy, the birth weights of children born to mothers who smoked up to nine cigarettes a day were 88 g (girls) and 107 g (boys) lower; in children born to mothers who smoked ≥ 10 cigarettes a day weights were 168 g and 247 g lower. At six months of age for the first group the mean weight for girls was 9 g (95% confidence interval -47 g to 65 g) higher and for boys 64 g (-118 g to -10 g) lower than that of children born to mothers who did not smoke. The corresponding figures for the second group were 28 g (-141 g to 85 g) lower for girls and 24 g (-136 g to 88 g) lower for boys. Conclusions - The deficits of weight at birth in children born to mothers who smoked during pregnancy are overcome by 6 months of age. These deficits are probably not permanent when smoking habit during pregnancy is not associated with other unfavourable variables (such as lower socioeconomic class).