Pre-Term Delivery and Risk of Ischemic Heart Disease in Women

Abstract

Background: Women who deliver pre-term have been reported to have increased future risks of cardiometabolic disorders. However, their long-term risks of ischemic heart disease (IHD) and whether such risks are due to shared familial factors are unclear. A better understanding of these risks may help improve long-term clinical follow-up and interventions to prevent IHD in women. Objectives: The purpose of this study was to determine the long-term risks of IHD in women by pregnancy duration. Methods: A national cohort study was conducted of all 2,189,190 women with a singleton delivery in Sweden from 1973 to 2015, who were followed up for IHD through the end of 2015. Cox regression was used to compute adjusted hazard ratios (aHRs) for IHD associated with pregnancy duration, and cosibling analyses assessed the influence of shared familial (genetic and/or environmental) factors. Results: In 47.5 million person-years of follow-up, 49,955 (2.3%) women were diagnosed with IHD. In the 10 years following delivery, the aHR for IHD associated with pre-term delivery (<37 weeks) was 2.47 (95% confidence interval [CI]: 2.16 to 2.82), and further stratified was 4.04 (95% CI: 2.69 to 6.08) for extremely pre-term (22 to 27 weeks), 2.62 (95% CI: 2.09 to 3.29) for very pre-term (28 to 33 weeks), 2.30 (95% CI: 1.97 to 2.70) for late pre-term (34 to 36 weeks), and 1.47 (95% CI: 1.30 to 1.65) for early-term (37 to 38 weeks), compared with full-term (39 to 41 weeks). These risks declined but remained significantly elevated after additional follow-up (pre-term vs. full-term, 10 to 19 years: aHR: 1.86; 95% CI: 1.73 to 1.99; 20 to 29 years: aHR: 1.52; 95% CI: 1.45 to 1.59; 30 to 43 years: aHR: 1.38; 95% CI: 1.32 to 1.45). These findings did not appear attributable to shared genetic or environmental factors within families. Additional pre-term deliveries were associated with further increases in risk. Conclusions: In this large national cohort, pre-term delivery was a strong independent risk factor for IHD. This association waned over time but remained substantially elevated up to 40 years later. Pre-term delivery should be recognized as a risk factor for IHD in women across the life course.