Association of parity with the timing and type of menopause: a longitudinal cohort study

We investigated the time-varying association between parity and timing of natural menopause, surgical menopause, and premenopausal hysterectomy among 23 728 women aged 40-65 years at enrollment in the Alberta's Tomorrow Project cohort study (2000-2022), using flexible parametric survival analysis. Overall, natural menopause was most common by study end (57.2%), followed by premenopausal hysterectomy (11.4%) and surgical menopause (5.3%). Risks of natural menopause before age 50 years were elevated for 0 births (adjusted hazard ratio [aHR] at age 45, 1.33; 95% CI, 1.18-1.49) and 1 birth (aHR age 45, 1.21; 95% CI, 1.07-1.38), but similar for ≥3 births (aHR age 45, 0.95; 95% CI, 0.85-1.06) compared to 2 births (reference). Elevated risks of surgical menopause before age 45 years for 0 births (aHR age 40, 1.37; 95% CI, 1.09-1.69) and 1 birth (aHR age 40, 1.11; 95% CI, 0.85-1.45) attenuated when excluding women with past infertility or recurrent pregnancy loss, and reduced risks were observed over time for ≥3 births (aHR age 50, 0.84; 95% CI, 0.75-0.94). Risks of premenopausal hysterectomy were lower before age 50 years for 0 births (aHR age 45, 0.82; 95% CI, 0.76-0.88) but elevated after age 40 years for ≥3 births (aHR age 50, 1.25; 95% CI, 1.08-1.45). These complex associations necessitate additional research on the sociobiological impacts of childbearing on gynecologic health.