Although heavier childhood body weight is a strong predictor of age at menarche,1 we did not adjust analyses for childhood body weight because it may be on the causal pathway between the exposures and age at menarche. Having been heavier than peers at age 10 was associated with maternal pre-pregnancy diabetes and with prenatal exposure to smoking, while having been lighter than peers at age 10 was associated with having a twin (or triplet) sibling (data not shown), which is consistent with childhood weight being on the causal pathway for age at menarche. However, pregnancy-related hypertensive disorder was weakly associated with both having been lighter and having been heavier than peers at age 10, and low birth weight was strongly associated with having been lighter than peers at age 10.
