Age of menarche in contemporary British teenagers: survey of girls born between 1982 and 1986

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Abstract
In 1998-9 we studied the cardiovascular health of secondary school children aged 12-16 in schools in 10 British towns: five in southern England (Esher, Leatherhead, Chelmsford, Bath, Tunbridge Wells), three in north west England (Wigan, Burnley, Rochdale), and two in south Wales (Port Talbot, Rhondda). We approached those secondary schools corresponding to a stratified random sample of primary schools in our earlier study3; 62 of 65 (95%) with female pupils participated. In each school we invited girls from the earlier study to participate, with a supplementary random sample of pupils from the same classes.3 During screening the girls completed a confidential self administered questionnaire on date of birth, whether they had started their periods and, if so, their age (years and months) at the first period. Social class was based on parental occupation (using the Registrar General's 1990 classification). Ethnicity was based on appearance and cross checked with surname and parental self assessment. We used SAS (version 6.12) for the statistical analysis. We determined the median age of menarche and confidence intervals using survival analysis with PROC LIFETEST. We included girls who had not yet had their first period (88 participants); for girls providing only year of menarche (231), the month was imputed using the mean value for other girls of the same age in years. Probit transformation2 of the percentage of affirmative responses at each age gave almost identical results. In all, 1166 girls aged 12-16 years (1068 European, 79 South Asian, 19 other) reported their menarcheal age (response 66%). The median menarcheal age was 12 years 11 months (95% confidence interval 12 years 10 months to 13 years 1 month). The percentages of girls who reported having had their first period by their 10th, 11th, or 12th birthdays were 0.8, 3.6 and 21.7, respectively; 11.8% had their first period before leaving primary school. Median ages of menarche were similar in different regions (table) and did not differ by social class or ethnic group (see table on website). Non-responders closely resembled responders in age and geographical location.