LENGTH AND VARIATION IN THE MENSTRUAL-CYCLE - A CROSS-SECTIONAL STUDY FROM A DANISH COUNTY

Objective To investigate the current epidemiology of menstrual patterns among women of fertile age. Design Cross-sectional postal questionnaire study. Setting County of Copenhagen, Denmark. Subjects 3743 women, aged 15-44, selected at random from a Danish county, who were asked to provide information on menstrual pattern during the preceding year, 198 1. 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.