Cardiovascular-kidney-metabolic syndrome and reproductive factors in postmenopausal Chinese and United States women: a cross-sectional analysis of two national survey cohorts

Abstract Background Whether female reproductive history is associated with cardiovascular-kidney-metabolic (CKM) syndrome staging and cardiometabolic multimorbidity, and whether such associations differ between populations, is unclear. We examined age at menarche, parity, and age at first birth in relation to these outcomes in two national cohorts of postmenopausal women in China and the United States. Methods We analyzed 3,876 women in China postmenopausal at the 2011 examination and 4,357 naturally postmenopausal United States women. Using harmonized definitions, including a modified CKM staging based on the American Heart Association framework, we estimated prevalence ratios (PRs) by modified Poisson regression for CKM stage ≥ 2 (primary), CKM stage ≥ 3, and cardiometabolic multimorbidity, and tested whether PRs differed between cohorts. Results Later menarche was associated with lower CKM stage ≥ 2 prevalence in both cohorts (China PR 0.985/year [95% CI 0.974–0.996]; United States 0.982 [0.969–0.995]), but survived correction in the United States only. Later age at first birth was associated with lower CKM stage ≥ 2 prevalence in the United States (0.991 [0.985–0.996]) but not in China (0.997 [0.992–1.003]). For multimorbidity, later menarche was associated with lower prevalence in the United States (0.919 [0.873–0.967], survived correction), whereas age at first birth showed only a nominal association in China (0.967 [0.940–0.994], not surviving correction). Parity was not associated with any outcome. Conclusions Later menarche was associated with lower CKM stage ≥ 2 prevalence in both cohorts, with similar magnitude, although this survived correction in the United States only; later age at first birth was associated with lower prevalence in the United States only. For multimorbidity, only later menarche in the United States survived correction. Parity was not associated with any outcome, and no cross-cohort difference survived correction. In these cross-sectional analyses, reproductive history appears to be a life-course marker of modest effect size, warranting prospective evaluation rather than causal or clinical use.