Timing of menarche in girls adopted from China: a cohort study

BACKGROUND: Girls adopted internationally from some states have been found to have high rates of early puberty, including early menarche. Explanations for the link between international adoption and early puberty include post-adoption catch-up growth triggering puberty, and under-recorded age. METHODS: We compared menarcheal age in a cohort of 814 girls adopted from China into North America against menarcheal ages in girls in China. Adoptive parents provided survey data on their daughters' weight in 2005 and on menarcheal status and age at menarche in 2011. RESULTS: Estimated median age at menarche for adopted Chinese girls is 12.37 years (95% CI: 11.84-13.00 years). Estimated prevalence of menarcheal age ≤10.00 years for adopted girls is 3%. These findings are similar to published findings on non-adopted Chinese girls. The distribution of menarche of adopted girls and non-adopted girls at the estimated incidence rates P3-P97 are also similar. Among the 609 girls whose parents reported on their weight shortly after adoption, 148 (24.3%) were -2SD or more below the median weight in the WHO weight-for-age tables. The proportion of these girls who had attained menarche was not statistically different from other girls. CONCLUSIONS: For girls adopted from China, the age of menarche, the percentage of girls attaining menarche <10 years and the distribution of menarcheal age are all similar to Chinese girls growing up in China.