Objective We analysed associations between gestational duration in grandchildren and their biological grandparents.
Methods The Uppsala Birth Cohort Multigenerational Study includes manually collected archive data on a representative cohort of males and females born in Uppsala, Sweden 1915–1929 and information on descendants of the cohort obtained through linkage to routine data registers. Using path analysis, we analysed 7915 grandparents and their 26 423 grandchildren, where the grandparent, the grandchild and the intermediate biological relation were singletons. Maternal grandmothers, maternal grandfathers, paternal grandmothers and paternal grandfathers were considered separately. Models were adjusted for social variables and fitted separately for male and female grandchildren due to evidence of effect modification by sex.
Results Gestational duration in grandparents was positively associated with gestational duration in their grandchildren. The observed direct effects are equivalent to a 0.3–0.4 (0.01≤p≤0.07) day increase in the grandchild's gestational duration for each additional week in the maternal grandparents' gestational duration and 0.1–0.2 (p≥0.2 in all models) day increase in the grandchild's gestational duration for each additional week in the paternal grandparents' gestational duration. Distinct and gender specific patterns of statistically significant associations were observed for risk of preterm and post-term birth across generations. Birthweight-for-gestational age in maternal grandfathers was positively associated with gestational duration in their grandchildren while birthweight-for-gestational age in paternal grandfathers was inversely related to gestational duration in their grandsons.
Conclusion Gestational duration in maternal grandparents is positively associated with gestational duration in their grandchildren. Birthweight-for-gestational age in paternal grandfathers influences gestational duration in their grandchildren negatively.
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