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

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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 35 days. At least one cycle length 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 5 days should be regarded as a sign of disease in the woman.