Expectancy of vacation as a determining factor of the annual rhythm of menarche Confirmación de la expectativa vacación-estudio como factor principal del ritmo anual de incidencia y edad de menarquia

Abstract

Background: Our previous studies have shown that the monthly rhythm of menarche is associated to the expectancy of holidays or vacations. If this hypothesis is true, menarche episodes in Chile should cluster in December, the month prior to summer vacations. Aim: To study whether the expectancy of holidays or vacations is the main determinant of the annual rhythm of menarche. Material and methods: During 1990 and 1991, a questionnaire about the date of birth and date of menarche, was applied to girls living in Santiago (Chile) and Medellin (Colombia), aged 8 to 18.5 years. They were requested to register the year, month or day of menarche, only if they recalled it precisely. Results: Discarding clerical errors, data was obtained from 3,225 Chilean and 3,435 Colombian girls. Of these 73 and 63% of Chilean and Colombian girls recalled the day of menarche. Among Chilean girls an excess of menarche episodes was observed in December, January and February. The mean age per month of menarche r