J Pediatr. 2005 Dec;147(6):753-60.


Interpreting the continued decline in the average age at menarche: results
from two nationally representative surveys of u.s. Girls studied 10 years
apart.

Anderson SE, Must A.

From the Gerald J. and Dorothy R. Friedman School of Nutrition Science and
Technology and the Department of Public Health and Family Medicine, Tufts
University, Boston, Massachusetts.

OBJECTIVES: To determine whether average age at menarche declined in the
United States during the past decade, and whether associations between
menarcheal timing, weight status, and race/ethnicity changed. STUDY DESIGN:
Relative weight, race/ethnicity, and menarcheal status of girls (n = 1577)
in the National Health and Nutrition Examination Survey (NHANES) III
(1988-1994) were compared with those of girls (n = 1720) in NHANES
1999-2002. Probit analysis estimated average age at menarche overall and
also by race/ethnicity. Logistic regression assessed associations of
relative weight and race/ethnicity with menarcheal status. RESULTS: In the
United States, average age at menarche declined from 12.53 years (95%
confidence interval [CI] = 12.43 to 12.63 years) in 1988-1994 to 12.34
years (95% CI = 12.24 to 12.45 years) in 1999-2002. By race/ethnicity,
average age at menarche estimates were as follows: non-Hispanic whites,
12.57 years (95% CI = 12.45 to 12.69 years) and 12.52 years (95% CI = 12.38
to 12.67 years); non-Hispanic blacks, 12.09 years (95% CI = 11.82 to 12.36
years) and 12.06 years (95% CI = 11.81 to 12.32 years); and Mexican
Americans, 12.24 years (95% CI = 11.88 to 12.59 years) and 12.09 years (95%
CI = 11.81 to 12.37 years). Higher relative weight was consistently
associated with increased likelihood of having reached menarche.
CONCLUSIONS: Average age at menarche in the United States declined by 2.3
months between 1988-1994 and 1999-2002; by race/ethnicity, declines were
considerably smaller. Changes in the population distribution of
race/ethnicity and relative weight should be considered when interpreting
trends in age at menarche.