Effects of early maturation on fetal growth

While the association of young maternal age with low birthweight (LBW) is well known, the contribution of early menarche to this association has never been studied. We examined the effects of early menarche (less than or equal to 11 years) on LBW and its two major underlying causes: pre-term delivery and smallness-for-gestational-age (SGA). Results represent a narrow chronological age range, 17-18 years, of a larger geographically based cohort of 2789 pregnant adolescents. Adjusted odds ratios (AOR) indicated that early menarche was significantly associated with an increased risk of LBW which was specific to SGA. The attributable risk of SGA with early menarche exceeded 20%. Early age at menarche is also correlated with an earlier onset of sexual activity, pregnancy, and childbearing. Consequently, adolescents with early menarche are over-represented in a sample limited to young gravidae or a sample that contains a stratum of young gravidae. This may have previously obscured the effects or early menarche on foetal growth and attributed them to a more frequently measured characteristic, young maternal age. Thus, effects of secular change in age at menarche may not be wholly benign. Improvements in maternal fertility and nutritional status appear to be offset by intrauterine growth retardation in the offspring.