Unilateral Oophorectomy and Age at Natural Menopause: A Longitudinal Community-Based Cohort Study.

Objective: To determine the association between unilateral oophorectomy (UO) and age at natural menopause.

Design: Secondary analysis of survey data from Alberta's Tomorrow Project (2000-2022).

Setting: Prospective cohort study in Alberta, Canada.

Population: 23 630 women; 548 experienced UO and 23 082 did not experience UO.

Methods: Flexible parametric survival analysis was used to analyse age at natural menopause, and logistic regression was used to analyse early menopause and premature ovarian insufficiency by UO status, controlling for birth year, parity, age at menarche, past infertility, hormonal contraceptive use and smoking.

Main outcome measures: Age at natural menopause occurred by a final menstrual period without medical cause and sub-classified as early menopause (< 45 years) and premature ovarian insufficiency (< 40 years).

Results: Compared to no UO, any UO was associated with elevated risk of earlier age at natural menopause, which was strongest in early midlife (adjusted HR at age 40 1.71, 95% CI 1.31-2.19) and diminished over time. Compared to age 55 years at UO, risks of earlier age at natural menopause were largest and uniform in magnitude when UO occurred between approximately ages 20-40 years (adjusted HR for UO at age 30 2.32, 1.46-3.54) and then diminished as age at UO approached the average age at natural menopause. Any UO was associated with higher odds of early menopause (adjusted OR 1.90, 1.30-2.79) and premature ovarian insufficiency (adjusted OR 3.75, 1.72-8.16).

Conclusions: Unilateral oophorectomy is associated with earlier age at natural menopause, particularly when performed before 40 years of age.