Preterm Delivery and Maternal Cardiovascular Disease

Abstract

Preterm delivery has been shown to be associated with a two-fold increased risk of maternal cardiovascular disease (CVD). However, it is unknown whether this risk persists after adjusting for pre-pregnancy lifestyle and CVD risk factors, including body mass index (BMI), smoking, and family history of CVD. Similarly, the extent to which this increased risk of CVD is accounted for by development of established CVD risk factors, and when these risk factors emerge, after a preterm delivery has not been assessed. Additionally, there is no evidence on the extent to which incorporating preterm delivery in CVD risk scores improves CVD risk prediction. Thus, we use the Nurses’ Health Study II to investigate associations of preterm delivery with CVD events and risk factors and the utility of including preterm delivery in CVD risk prediction. In Chapter 1, we evaluate the association between preterm delivery and CVD and the proportion accounted for by postpartum development of CVD risk factors. Women who delivered their first infant preterm had a 42% increased rate of CVD while those who delivered before 32 weeks experienced a doubling of risk. Only a modest proportion (13.1%) of the very preterm-CVD association was accounted for by development of traditional CVD risk factors. In Chapter 2, we investigate associations between preterm delivery and CVD risk factors. Preterm delivery in first birth was associated with an 11% increased rate of chronic hypertension, 17% increased rate of type 2 diabetes mellitus, and 7% increased rate of hypercholesterolemia; this was generally stronger in women who delivered very preterm and within the first 10 years after delivery. In Chapter 3, we test the utility of including preterm delivery and parity into CVD risk prediction models. Incorporation of preterm delivery and parity improved model fit in 10- and 20-year models, but only resulted in small improvements in discrimination and net reclassification of women with CVD events in 20-year models at age ≥30 years. Together, these results suggest that preterm delivery may serve as a marker of women at high-risk of CVD that can be used to target prevention and screening efforts, particularly when women are young.