Introduction: The proximal aorta has been shown to enlarge with aging in humans, but the long-term impact of hormonal and hemodynamic changes associated with pregnancy on aortic size and function are unknown. We examined if number of live births was independently associated with aortic dimensions and stiffness in a healthy multi-ethnic population-based cohort, the Dallas Heart Study (DHS). We hypothesized that multiparity (>/=4 live births) is independently associated with aortic dilation and aortic stiffness after adjustment for CV risk factors. Methods: Women with available thoracic aortic MRI measurements (n=1468, mean 44.5 years old) from DHS were stratified based on self-reported number of live births (0,1,2,3,>/=4). Sequential multivariable logistic regression models were used to assess independent associations of the number of live births with ascending aortic cross-sectional area/height, aortic pulse wave velocity (PWV) and aortic compliance. Models were adjusted for major CV risk factors. Results: Women with >/=4 live births were older, more likely to be Black, and had higher blood pressure, triglycerides and body mass index. Compared with nulliparous women, women with >/=4 had larger ascending aortic areas indexed to height [5.19 vs 4.74 cm2/m; p<0.0001; Table 1]. After adjustment for risk factors, multiparity remained a significant predictor of aortic size. Compared to nulliparous women, women with >/=4 live births also had higher aortic PWV (5.54 vs 4.54 m/s; p<0.0001) and lower aortic compliance (21.9 vs 27.2 mL/mmHg; p 0.0002), but these relationships were no longer significant after multivariable adjustment (Table 1). Analyzing live births as a continuous variable did not change these results. Conclusions: Multiparity was associated with thoracic aortic enlargement, independent of age and relevant risk factors. Parity is an emerging sex-specific risk factor in cardiovascular disease that may have an impact on aortic remodeling in women.