Five previous studies found associations between prenatal exposure to maternal smoking and younger age at menarche,8,10-13 with two of these studies reporting associations specifically with smoking in the third trimester10 and heavy smoking of at least a pack of cigarettes a day.8 Two studies in predominantly black or multiethnic cohorts reported an association with later age at menarche and heavy maternal smoking.9,14 Although we had no information on smoking frequency or timing during pregnancy, our finding of an association between maternal smoking and early menarche was consistent with other studies in predominantly white cohorts.8,10-13 It is also possible that the association with prenatal exposure to smoking may be confounded by maternal age at menarche if mothers with early menarche were more likely to become smokers and have daughters with early menarche. However, associations between prenatal exposure to smoking and early menarche remained in three of the studies after adjustment for maternal age at menarche.8,10,11
