Women who deliver preterm are at an increased risk of developing ischemic heart disease (IHD) over the course of their life, independent of other risk factors such as BMI or smoking, according to a study published June 29 in the Journal of the American College of Cardiology.

Casey Crump, MD, PhD, and colleagues used the Swedish Medical Birth Registry to determine long-term changes in IHD risks in women who gave birth, with up to 43 years of follow-up. They examined data from 2,189,190 women who had singleton deliveries between 1973 and 2015. Co-sibling analyses were also performed among 1,188,730 women (54.3%), with at least one sister who had a singleton delivery.

The pregnancy duration was split into six groups: extremely preterm (22-27 weeks), very preterm (28-33 weeks), late preterm (34-36 weeks), early term (37-38 weeks), full-term (39-41 weeks; study reference group) and post-term (42 weeks or more). Additionally, the extremely, very and late preterm groups were combined to provide summary risk estimates for preterm delivery.

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 increased risk for IHD was approximately 2.5- and 4-fold higher, respectively, in women who delivered preterm or extremely preterm, compared with full-term delivery, after adjusting for preeclampsia, diabetes, high BMI and smoking. Early-term delivery also was associated with an increased risk of IHD (approximately 1.4-fold). These risks subsequently declined but remained significantly elevated even 30-43 years after delivery.

According to the authors, this is the first study to assess the potential influence of unmeasured familial factors on associations between preterm delivery and future maternal risk of IHD. Results from the co-sibling analyses suggested these findings were not attributable to shared genetic or environmental factors in families.

"Preterm delivery should now be recognized as an independent risk factor for IHD across the life course," said Crump. "The findings suggest that preterm and early-term delivery are important independent risk factors for the development of IHD, and that the associated risks may persist up to 40 years later. Women who deliver prematurely need early preventive evaluation and long-term monitoring for IHD."

Among the limitations of the study are the lack of detailed clinical data to verify IHD diagnoses and the possibility that confounding factors, such as maternal smoking, BMI or other IHD risk factors during pregnancy, were not completely controlled. Preterm delivery occurs in about 9.6% of births in the U.S. annually. However, this study was limited to Sweden, and will need to be replicated in other countries, including racially diverse populations to explore for potential heterogeneity of findings.

In an accompanying editorial comment, Anne Marie Valente, MD, FACC, and colleagues, wrote, "The higher IHD risk in women who had preterm birth persisted in co-sibling analysis, suggesting that shared genetic or environmental factors did not underlie the association with IHD. The novel results are a call to action for further development of the field of cardio-obstetrics."

Clinical Topics: Prevention, Smoking

Keywords: Pregnancy, Risk Factors, Obstetrics, Premature Birth, Parturition, Registries, Myocardial Ischemia, Smoking, Diabetes Mellitus

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