Objective: To investigate the influences on birth weight of maternal smoking during pregnancy across generations.
Design: Intergenerational cohort study.
Participants: Members of the 1958 birth cohort and their offspring and mothers.
Setting: England, Scotland, and Wales.
Main outcome measure: Birth weight.
Results: Information on grandmothers' smoking during pregnancy was available for 9028 singleton offspring of 4302 female cohort members. Assuming heritable transmission through the intergenerational association, grandmothers' smoking was predicted to result in a 34 g reduction (95% confidence interval -41 g to -28 g) in the birth weight of grandchildren. Random effects models showed a negative association between grandmothers' smoking and birth weight of grandchildren (beta regression coefficient -24 g, -50 g to 3 g), but this effect was eliminated after adjustment for maternal smoking (0 g, -26 g to 26 g). No association was evident among the offspring of non-smoking mothers (n = 6105; 14 g, -17 g to 46 g), and after adjustment for maternal birth weight, adult height and body mass index, grandmothers' smoking was positively associated with the birth weight of grandchildren (45 g, 10 g to 80 g).
Conclusion: Deficits in mothers' birth weight attributable to their mother smoking was not evident in the grandchildren.