Preterm Delivery Raises Lifetime Hypertension Risk

Heidi Splete

October 20, 2021

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 City, 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 January 1, 1973, to December 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 [aHR], 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 (aHR, 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.

Data Highlight the Need for Patient and Provider Education

"This study furthers our knowledge regarding long-term complications associated with the frequent pregnancy complication of preterm delivery," Stephen S. Crane, MD, an OB-GYN. and maternal-fetal medicine specialist in private practice in Orlando, said in an interview. "Cardiovascular disease is the leading cause of death and often goes unrecognized in women. There are shared risk factors among women and men for developing CVD, the most common being hypertension. However, women have the unique risk factor of pregnancy and its attendant complications including preeclampsia, glucose intolerance, and preterm delivery. Hypertensive disorders in pregnancy often lead to indicated premature delivery, and are associated with development of chronic hypertension and subsequent CVD. However, prior data suggest that preterm delivery itself is a risk factor for developing chronic hypertension later in life.

"The current study, which evaluates one of the most complete population data sets with up to 43 years of follow-up, is the first to assess for familial determinants by cosibling analysis, and supports preterm delivery as an independent risk factor for the development of hypertension," he said. The study results illustrate that this risk is longstanding, and that recurrent preterm birth further increases the risk of developing hypertension.

Crane said he was not surprised by the study findings, given that inflammatory processes have been linked to the development of hypertension and CVD. "Similarly, inflammatory processes have been implicated in the pathophysiology of preterm labor and inflammatory cytokines may also play a role in normal term labor. Therefore, it is not surprising that preterm delivery would be a marker for the risk of development of hypertension, as both may be responses to underlying inflammatory processes. Identification of these underlying inflammatory processes and methods for prevention will be critical if we are to decrease both the incidence of preterm birth and CVD.

"As prenatal care may be the only medical care women obtain, it is important to take this opportunity to educate patients regarding their long-term risks of developing hypertension and the need for long-term follow-up. Interventions that may help reduce the risk for recurrent preterm birth and long-term risks for developing hypertension and CVD include weight loss, increased activity, and smoking cessation; the resources to achieve these goals need to be shared with patients," he said.

"Knowledge deficits both on the part of the provider and patient may be a significant barrier to intervention that may be overcome with improved education," said Crane. "Care providers need education regarding the long-term risks associated with a history of preterm delivery in order to better educate their patients regarding both prevention of recurrent preterm birth and the development of hypertension and CVD." However, socioeconomic status, education level, and the inability to obtain further healthcare remain common barriers to intervention for many women.

"Additional research is needed to identify the causes of inflammatory processes leading to preterm delivery and risks for hypertension and CVD," said Crane. "Only after the causes are identified can treatments be sought to successfully treat these conditions."

The study was supported by the National Heart, Lung, and Blood Institute at the National Institutes of Health; the Swedish Research Council; the Swedish Heart-Lung Foundation; and an Avtal om Läkarutbildning och Forskning (Agreement on Medical Training and Research) (ALF) project grant from Region Skåne/Lund University. Neither the researchers nor Crane have disclosed any relevant financial relationships.

JAMA Cardiol. Published online October 13, 2021. Abstract

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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