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We sought to determine which factors influence the association between menarche and conception among adolescent study participants (n=1030), who demonstrated an earlier age of menarche than did national samples. Age at first sexual intercourse (coitarche) mediated the relationship between age at menarche and first pregnancy among White girls, whereas gynecologic age at coitarche (age at coitarche minus age at menarche) and age at menarche explained the timing of the first pregnancy among Black and Hispanic girls. Pregnancy prevention interventions to delay coitarche should also include reproductive education and contraception. (Am J Public Health. 2008;98:1822-1824. doi:10.2105/AJPH.2007.120444)
Early-maturing females tend to become pregnant at younger ages than do later-maturing females.1-4 Speculations about this nonrandom association include the effect of sex hormones,5 the schism between rapid physical development and cognitive and psychosocialmaturity,6-13 and genetic influences.14-26 Given the trend toward earlier menarche27-29 and the desirability of preventing adolescent childbearing,22,30,31a better understanding of the underlyingmechanisms could improve pregnancy prevention interventions for young adolescent girls.
Among nulligravid American girls, Black females tend to mature at an earlier age than do Hispanic and White girls.27-29 However, a report by Deardorff et al.6 indicates that pregnant Black adolescents had a later menarche than did White adolescents. Whereas the age at menarche for White participants was early by US standards, the age at menarche for Black participants was not.6,27-29 This unanticipated finding is intriguing and motivated this analysis.
We speculated that early physical maturation is not an important antecedent of early childbearing among Black Americans because the prime mediator of the relationship between early menarche and early pregnancy, early age at coitarche,6 is more normative among Black than among White American girls.30 Accordingly, we tested the hypothesis that in a cohort of pregnant adolescents, coitarche explains the association between menarche and first pregnancy among White girls, but fecundity (i.e., fertility) at coitarche underlies the association between these two events among Black and Hispanic girls.
METHODS
Study participants were a racially and ethnically diverse group (31.4% White, 29.9% Black, and 38.7% Hispanic) of 1030 pregnant, primigravid adolescents aged 13 to 18 years. The primary source of data was the Electronic Report on Adolescent Pregnancy of the Colorado Adolescent Maternity Program.32
Age at menarche was self-reported, and early menarche was defined as age 10 years...