Contributions of Preterm Delivery to Cardiovascular Disease Risk Prediction in Women

Preterm delivery is associated with a 1.4- to 2-fold increased risk of cardiovascular disease (CVD), but inclusion of preterm delivery in CVD risk prediction algorithms has not been tested. We evaluated whether including preterm delivery and parity in CVD risk scores improved identification of women at high risk versus scores based on traditional risk factors. We predicted 10-year CVD risk using 119,587 observations contributed by 76,512 women ≥40 years of age and 20-year CVD risk with 72,533 women ≥40 years of age and 72,872 women ≥30 years of age from the Nurses' Health Study II. Cox proportional hazards models were fit with established CVD risk factors (Model 1) and established risk factors plus preterm delivery and parity (Model 2). We evaluated model fit, calibration, discrimination, and risk reclassification. Very preterm delivery (<32 weeks) was associated with CVD in all 10- and 20-year models that included the established CVD risk factors (e.g., hazard ratio: 1.61, 95% confidence interval: 1.19 to 2.20 in 10-year risk model). Model 2 had improved fit relative to Model 1, but discrimination was not improved in Model 2 based on the C-difference or net reclassification index. Similar models for 20-year CVD risk prediction at age ≥30 years indicated improved discrimination when including preterm delivery and parity. Incorporating preterm delivery and parity into CVD risk scores appears most useful when women are young, before they develop established CVD risk factors. Observed improvements in risk prediction were small and warrant further investigation to confirm our findings and assess utility in a clinical setting.