Reproductive characteristics and the age at inception of the perimenopausein a British National Cohort

Data from a British national cohort of women born in 1946 were used to inve stigate the hypothesis that the rate of depletion of oocyte numbers is asso ciated with the age at which a woman reaches the inception of the perimenop ause. Menopausal status was obtained using an annual questionnaire, sent to the cohort since the age of 47 years, and risk factor information from con tacts with the survey throughout earlier life. Parous women entered the per imenopause later than nulliparous women. Those with the most children had t he latest perimenopause, where the estimated hazard ratio for women having four or more children compared with those having none was 0.56 (95% confide nce interval 0.39-0.81). Women who had a unilateral oophorectomy reached pe rimenopause earlier then those who had not (hazard ratio = 1.96, 95% confid ence interval 1.15-3.35), There was some evidence that early age at menarch e and short menstrual cycles were associated with an earlier perimenopause. No relation was observed with oral contraceptive pill use. Results provide d some support for the hypothesis under consideration, while estimates of t he median age at inception of the perimenopause due to these factors ranged from 46 to 50 years, which is an important variation with respect to later health.