[Factors possibly associated with the age at the onset of menopause. Multicenter study]

A transversal study was performed in 1987 to examine 9,844 postmenopausal women aging from 39 to 59 years, residents from the cities of Durango, Monterrey, Guadalajara and Leon. They had their last menstruation at least 12 months before the interview and they were not pregnant. The objective was to know if the menarche, number of deliveries, use of contraceptive methods and smoking could affect the age of menopause. A case control analysis was performed. Based on frequency distribution of the age on which the menopause appeared, cases were classified as early and late menopause when a median value minus 2 SD and plus 2 SD were found, respectively. For control subjects a median + 1 SD was selected. Two and three controls were randomly assigned for early and late menopause, respectively. In total 1,610 subjects were studied. As a measure of association it was used the odds ratio with a confidence level of 95%. It was performed an analysis of confusion and interaction of variables in this study. The most relevant results were; a significant association between smoking 15 packages of cigarettes a year with an OR of 2.31 (1.05-5.17), to have more than five pregnancies with an OR of Mantel and Haenzel of 0.51 (0.33-0.76) for the early menopause. No association with late menopause was observed. It was found that the mean age of menopause was 45.5 years + 4.5 SD (n = 9,844).