Length and variation in the menstrual cycle--a cross-sectional study from a Danish county

Abstract

Objective To investigate the current epidemiology of menstrual patters among women of fertile age. Design Cross‐sectional postal questionnaire study. Setting County of Copenhagen, Denmark. Subjects 3743 women, aged 15–14, selected at random from a Danish county, who were asked to provide information on menstrual pattern during the preceding year, 1981. The response rate was 78%. Information from non‐responders was obtained via telephone interviews. Results In women with regular menstrual cycles, the 5th–95th centile range of usual cycle length decreased from 23–35 days in the 15–19 years age group to 23–30 days in the 40–44 years age group. Only 0.5% of regular menstruating women had a usual cycle length of <21 days and 0.9% had a usual cycle length of >35 days. At least one cycle length of <21 days was experienced by 18.6%, whereas 29.5% had at least one cycle of >35 days. Menstrual cycle variation of >14 days was present in 29.3% of all women. Cycle length variation of > 14 days was 2.7 times more frequent in women from lower social groups (controlled by age). Conclusion The study confirmed the normally used definitions of polymenorrhoea (cycle length <21 days) and oligomenorrhoea (cycle length between 36 and 90 days), as these very short or long menstrual cycle lengths were very seldom recorded for a longer period. However, the high frequency in a normal population of large menstrual cycle length variation challenges the view that an intra‐individual variation of >5 days should be regarded as a sign of disease in the woman.