The natural history of primary dysmenorrhoea: a longitudinal study.

OBJECTIVE: To describe the prevalence, severity, course and predictive factors of primary dysmenorrhoea in women of all reproductive ages.

DESIGN: Prospective mailed surveys in 1985 and 1991.

SETTING: University of Iowa, College of Nursing.

POPULATION: We began with a stratified sample of 996 nurses who graduated between 1963 and 1984. We analysed data from 404 women who responded to both surveys, but denied endometriosis, pelvic inflammatory disease or uterine fibroids.

METHODS: Participants were surveyed twice at an interval of six years (response rates 73% and 78%) regarding menstrual cycle characteristics. For analysis, dysmenorrhoea was dichotomised as none/mild or moderate/severe. We analysed predictive factors using chi2 tests and stepwise logistic regression.

MAIN OUTCOME MEASURE: Severity of dysmenorrhoea. Menstrual cramps as experienced when not taking medication to prevent discomfort were rated on a four-point scale: 0 = no dysmenorrhoea, 1 = minimal (can work, somewhat uncomfortable), 2 = moderate (can work, but quite uncomfortable) or 3 = severe dysmenorrhoea (miss work, have to be in bed).

RESULTS: In 1985, 80% of respondents were >25 years old and 60% were parous. There were few changes over six years in the prevalence of mild (51% to 53%), moderate (22% to 20%) or severe dysmenorrhoea (4% to 2%). After adjusting for dysmenorrhoea in 1985, each live birth during follow up (OR = 0.20, 95% CI = 0.08 to 0.53) and older age (OR = 0.92, 95% CI = 0.86 to 0.98) were associated with less dysmenorrhoea in 1991.

CONCLUSIONS: Primary dysmenorrhoea affects most women throughout the menstrual years. Dysmenorrhoea severe enough to cause absence from work occurs in less than 5% of women. Although improvement and worsening are equally likely for all women, improvement is more likely in women who bear children.