Parity, Age at Childbirth, and Later-Life Maternal Cardiovascular Disease in Postmenopausal Women in the Women's Health Initiative Study

OBJECTIVE: To examine the associations of parity and age at childbirth with maternal cardiovascular disease (CVD). METHODS: The data were from the Women's Health Initiative (1993–2022), involving postmenopausal women aged 49–81 years without existing CVD. The exposures were parity, age at first childbirth, and age at last childbirth, all referring to pregnancy lasting at least 6 months. The outcome was incident CVD events , defined as the initial occurrence of coronary heart disease, heart failure, ischemic stroke, or death due to these conditions. We employed propensity score matching to generate matched samples, aligning each exposure group with a reference group according to their propensity scores. We used multilevel Cox proportional hazard models to calculate hazard ratios (HRs) and 95% CIs to estimate the associations among parity, age at childbirth, and CVD. We performed multiple mediation analyses to assess the effect of potential mediators on the associations. RESULTS: Compared with parity of two, there was no significant association between other parity levels and later-life maternal CVD. Compared with age at first childbirth of 25–29 years, the HRs (95% CIs) for the association between CVD and age at first childbirth was 1.32 (1.22–1.44) for individuals younger than age 20 years, 1.11 (1.05–1.17) for those aged 20–24 years, 1.03 (0.93–1.13) for those aged 30–34 years, and 0.93 (0.79–1.11) for those aged 35 years or older. When age at last childbirth was younger than 25 years, 30–34 years, 35–39 years, and 40 years or older, the HRs (95% CIs) for CVD were 1.02 (0.94–1.10), 1.05 (0.99–1.10), 1.10 (1.03–1.18), and 1.09 (0.96–1.24), respectively. In multiple mediation analyses, we identified the potential mediation pathway of age at first childbirth younger than 25 years→premature menopause→hypertension→CVD. CONCLUSION: Young age at first childbirth was associated with increased maternal CVD risk. Preventing premature menopause and hypertension may be important ways to lower the risk for postmenopausal women.