Is unilateral oophorectomy associated with age at menopause? A population study (the HUNT2 Survey).

STUDY QUESTION Is unilateral oophorectomy associated with age at menopause? SUMMARY ANSWER Women who had undergone unilateral oophorectomy entered menopause 1 year earlier than women with two ovaries intact. WHAT IS ALREADY KNOWN There is substantial variation in age at natural menopause. Unilateral oophorectomy implies a significant reduction of the ovarian follicular reserve. Thus, one might expect that the time to menopause is shortened by several years in women who have undergone unilateral oophorectomy. STUDY DESIGN, SIZE AND DURATION A retrospective cohort study of 23 580 Norwegian women who were included in the population-based HUNT2 Survey during the years 1995-1997. PARTICIPANTS/MATERIALS, SETTING, METHODS Data were obtained by two self-administered questionnaires at study inclusion. Cox proportional hazard models were used to estimate relative risks of menopause according to unilateral oophorectomy status with and without adjustment for birth cohort, parity, smoking, body mass index (BMI) and age at menarche. MAIN RESULTS AND THE ROLE OF CHANCE Women who had undergone unilateral oophorectomy were younger at menopause [mean 49.6 years; 95% confidence interval (CI): 49.2-50.0] than women without unilateral oophorectomy (mean 50.7 years; 95% CI: 50.6-50.8) (P < 0.001). The crude relative risk of menopause was 1.28 (95% CI: 1.15-1.42) and remained similar after adjustment for the study factors above (adjusted relative risk 1.27; 95% CI: 1.14-1.41). In addition, recent birth cohort and high BMI were associated with higher age at menopause. LIMITATIONS, REASONS FOR CAUTION Information on unilateral oophorectomy was based on self-reports. Some women may therefore have been misclassified. WIDER IMPLICATIONS OF THE FINDINGS Although the effect of unilateral oophorectomy on the age at menopause is similar to that of smoking, it is weaker than anticipated from the loss of ovarian follicular reserve. Thus, compensatory mechanisms may occur in the remaining ovary.