Women who had a preterm delivery were at least 1.6 times as likely to develop hypertension over the next decade as those who had full-term deliveries, based on data from a national cohort study of more than 2 million women.
Pregnancy complications such as preeclampsia and other hypertensive disorders of pregnancy have been associated with chronic hypertension as well as with preterm delivery, but the independent role of preterm delivery in chronic hypertension risk remains unclear, Casey Crump, MD, of the Icahn School of Medicine at Mount Sinai, New York, and colleagues wrote. “A better understanding of the long-term hypertension risks associated with preterm delivery is needed to improve risk stratification, clinical monitoring, and CVD [cardiovascular disease] prevention in women.”
In a study published in JAMA Cardiology, the researchers reviewed data from 2,195,989 women with 4,308,286 singleton deliveries in Sweden from Jan. 1, 1973, to Dec. 31, 2015. Women with preexisting hypertension before their first pregnancy were excluded. Pregnancy duration was based on maternal reports of the last menstrual period for patients in the 1970s, and based on ultrasound estimates in the 1980s and beyond. Pregnancy duration was divided into six groups in terms of completed weeks of gestation: extremely preterm (22-27 weeks), moderately preterm (28-33 weeks), late preterm (34-36 weeks), early term (37-38 weeks), full term (39-41 weeks), and post term (≥42 weeks). Full-term delivery was used as the reference, and the three preterm groups were combined for summaries of preterm delivery (less than 37 weeks).
Overall, women who delivered at less than 37 weeks’ gestation had a 1.6-fold increased risk of hypertension (adjusted hazard ratio, 1.67) within the next 10 years, compared with women who delivered full term after controlling for preeclampsia, other hypertensive disorders of pregnancy, and maternal factors.
When further stratified by pregnancy duration, the aHRs for extremely preterm, moderately preterm, late preterm, and early term, compared with full-term deliveries were 2.23, 1.85, 1.55, and 1.26, respectively, in the first decade after delivery. Each additional week of pregnancy was associated with a mean 7% reduction in hypertension risk (a HR, 0.93).
The increased hypertension risk following preterm delivery (less than 37 weeks) persisted at 10-19 years, 20-29 years, and 30-43 years, with aHRs of 1.40, 1.20, and 1.12, respectively. Early-term delivery at 37-38 weeks also carried an increased risk of long-term hypertension compared with full-term delivery, with aHRs of 1.12 and 1.06 at 20-29 years and 30-43 years, respectively.
“Cosibling analyses suggested that these findings were only partially explained by familial (genetic and/or early-life environmental) factors that are shared determinants of both preterm delivery and hypertension,” the researchers noted. The findings suggest that preterm delivery itself may contribute to or affect the pathophysiology that leads to cardiovascular disease, they added, hypothesizing that endothelial dysfunction caused by preterm delivery may cause functional impairments in the microvasculature.
The study findings were limited by several factors including the lack of detailed records to verify hypertension and the use of data from a single country, the researchers noted. However, the results were strengthened by the large study population, the use of highly complete prenatal and birth records to minimize selection bias, and the long-term follow-up.
The results are consistent with those from previous studies, and support the recognition of preterm delivery as a lifetime risk factor for hypertension, but future studies should focus on racial and ethnic subgroups already at increased risk for both preterm delivery and hypertension, they added.
“Additional follow-up will be needed to examine these associations in older adulthood when hypertension increasingly and disproportionately affects women,” they concluded.