Women who had a preterm delivery during their first pregnancy had a 54 percent increased risk of cardiovascular disease compared with women who had a term delivery in their first pregnancy, according to an analysis of a longitudinal study.

After adjusting prepregnancy lifestyle and cardiovascular disease risk factors, women who had a preterm delivery still had a 42 percent increased risk of cardiovascular disease.

The researchers defined preterm delivery as less than 37 weeks after getting pregnant and term delivery as 37 weeks or later. Approximately 10 percent of pregnancies each year in the U.S. are preterm.

Lead researcher Lauren J. Tanz, MSPH, of the Harvard T.H. Chan School of Public Health and Brigham and Women’s Hospital in Boston, and colleagues published their results online in Circulation on Feb. 2.

“Delivering a preterm infant may be an early warning signal of high risk for cardiovascular disease,” Tanz said in a news release. “Since cardiovascular risk develops over a lifetime, it’s not too early for these women to adopt a heart healthy lifestyle.”

This analysis included 70,182 women who were part of the Nurses’ Health Study II, which enrolled nurses who were 25 to 42 years old at baseline in 1989. The women completed biennial questionnaires on diet, physical activity, smoking, medications, reproductive history and incident disease. In addition, more than 91,000 were sent a questionnaire in 2001 asking about their pregnancy history. All participants also received a questionnaire in 2009 about their pregnancy history.

Of the participants, 91.2 percent delivered at term in their first pregnancy and nearly 9 percent delivered preterm, including 2.1 percent who delivered very preterm and 6.7 percent who delivered moderately preterm. The researchers defined very preterm as less than 32 weeks and moderately preterm as between 32 and 37 weeks.

Women who delivered preterm were slightly more likely to have a body mass index of 30 kg/m² or higher, prepregnancy hypertension and hypercholesterolemia and a family history of cardiovascular disease. Women who delivered very preterm were more likely to be current smokers, experience a stillbirth in their first pregnancy and have higher final parity.

During a median follow-up period of 32 years, there were 949 cardiovascular disease events (MIs and strokes), of which 584 were considered definite and 365 were considered probable.

After adjusting for prepregnancy sociodemographic, lifestyle and cardiovascular disease risk factors, women who had a moderate preterm delivery had a 22 percent increased risk of cardiovascular disease, while women who had a very preterm delivery had more than double the risk of cardiovascular disease compared with women who had a term delivery.

The results were similar when the researchers adjusted for prepregnancy miscarriage, when they expanded the outcome to include coronary revascularization and when they excluded multiple gestation pregnancies.

The researchers mentioned a few limitations of the study, including that participants self-reported their gestation length a median 27 years after delivery, which could have led to misclassification. They also said the results could be subject to residual and unmeasured confounding. In addition, 93 percent of the women were white, so the findings might not be generalizable to other races or ethnicities.

“We need further research to determine the incidence and timing of the development of these risk factors and establish the most effective screening and prevention protocols for women with a history of preterm delivery,” the researchers wrote. “We also need additional research on alternative, novel pathways through which preterm and [cardiovascular disease] may be associated and which could also inform prevention methods. Ultimately, preterm delivery may be a useful prognostic tool to identify high-risk women early in life who would benefit from early screening, prevention, and treatment.”