Early or recurrent preterm birth and maternal cardiovascular disease risk

Preterm birth (PTB) has been associated with a later increased risk of maternal cardiovascular disease (CVD). We hypothesized a more pronounced relation between early or recurrent PTB and maternal CVD risk.

We related PTB severity (earlier gestational age at delivery) and recurrence (>/=2) among women with births from 1973-1983 in Denmark (n = 427,765) to maternal CVD morbidity or mortality (1977-2006). Birth data were linked to CVD hospitalizations and deaths identified in national registers and data were analyzed using Cox proportional hazards models.

Women with a prior PTB had excess CVD after adjustment for age, parity, and education (hazard ratio [HR] = 1.36 [95% confidence interval (CI): 1.31, 1.41]). This was only modestly attenuated when women with preeclampsia or small for gestational age births were excluded, and the relationship was stronger for CVD mortality (HR = 1.98 [1.73, 2.26]). Recurrent PTB was associated with higher CVD morbidity compared to women with one PTB, particularly for ischemic events (HR = 1.78 [1.40, 2.27] vs. 1.22 [1.09, 1.36]). Risk was similarly elevated among women with early, moderate, and late PTB. Sensitivity analysis suggested that confounding by smoking only partly explained these associations.

Women with PTB, especially recurrent PTB, were at increased risk for CVD, suggesting common causes of these conditions.