Maternal Birth Weight and BMI Mediate the Transgenerational Effect of Grandmaternal BMI on Grandchild’s Birth Weight


Objective: The aims of this study are to examine the potential association between grandmaternal BMI and grandchild’s birth weight (BW) and whether maternal BW and BMI mediate this association. Methods: Data of 209 grandmother-mother pairs and 355 grandchildren from the Isle of Wight birth cohort in the UK were analyzed using path analysis. Results: An indirect effect of grandmaternal BMI on increasing grandchild’s BW was mediated by maternal BW and BMI at age 18 years (indirect effects: β = 2.3 g/unit increase in grandmaternal BMI via maternal BW and β = 4.4 g via maternal BMI; P = 0.04). These two mediating effects of maternal BW and BMI confounded one another. Grandmaternal smoking during pregnancy had an indirect effect on decreasing grandchild’s BW, dependent on maternal smoking during pregnancy and BW (indirect effects: β = −36.1 g compared with nonsmoking grandmothers via maternal smoking during pregnancy and β = −27.2 g via maternal BW; P = 0.005). Neither direct effect between grandmaternal BMI and grandchild’s BW nor that between grandmaternal smoking during pregnancy and grandchild’s BW was statistically significant. Conclusions: Larger grandmaternal BMI indirectly increased grandchild’s BW via maternal BW and BMI. Grandmaternal smoking during pregnancy indirectly reduced grandchild’s BW via maternal smoking during pregnancy and BW.

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