Maternal smoking during pregnancy and birthweight on the third generation: results from two birth cohort studies

The purpose of this research is to investigate whether grandmother's smoking during pregnancy reduces the grandchildren's birthweight and whether maternal smoking during pregnancy modified this association. We also evaluated the effect of duration and intensity of smoking. This study included data from three generations from two birth cohorts carried out in Pelotas, a southern Brazilian city: women enrolled in the perinatal study in the 1982 and 1993 cohorts (G1); daughters (G2) of those G1 mothers who were followed to adulthood; and first children (G3) born from G2 women. Information on maternal smoking during pregnancy was obtained from women (G1) shortly after delivery of the two cohorts and from G2 in the follow-up in adulthood of the 1993 cohort. Mothers (G2) reported G3 birthweight during the follow-up visit at adulthood. Multiple linear regression was used to obtain effect measures adjusted for confounders. The study included 1602 grandmothers (G1), mothers (G2), and grandchildren (G3). Prevalence of maternal (G1) smoking during pregnancy was 43% and mean G3 birthweight was 3118.9 g (SD: 608.8). Grandmother's smoking in the pregnancy was not associated with grandchild's birthweight. However, offspring of both G1 and G2 smokers had lower mean birthweight than those whose mother and grandmother did not smoke (adjusted β: - 223.05; 95% CI: - 415.16, - 32.76).

No significant association was observed between grandmother's smoking in the pregnancy and grandchild's birthweight. But it seems that grandmother's smoking in pregnancy has an effect on grandchild's birthweight when the mother also smoked in the pregnancy. .

• Most studies on the association of maternal tobacco smoking in pregnancy with offspring birthweight have been restricted to two generations, and an inverse association is well known.

• Besides to investigate whether grandmother's smoking during pregnancy reduces the grandchildren's birthweight, we examined whether this association varied according to maternal smoking during pregnancy.