Shorter Pregnancies Mean Higher Lifelong Hypertension Risk

Delivering a child preterm carried lifelong risk for hypertension, a large population-based study showed.

Among more than 2 million women in Sweden, delivery before 37 weeks’ gestation was independently associated with a 1.67-fold increased risk (95% CI 1.61-1.74) of developing hypertension in the following 10 years, reported Casey Crump, MD, PhD, of Icahn School of Medicine at Mount Sinai in New York City, and colleagues in JAMA Cardiology.

The risk was highest for the most preterm deliveries, but adjusted hazard ratios were significant for every category compared with a full 39 to 41 weeks’ gestation:

• 2.23 (95% CI 1.98-2.52) for extremely preterm delivery at 22 to 27 weeks
• 1.85 (95% CI 1.74-1.97) for moderately preterm delivery at 28 to 33 weeks
• 1.55 (95% CI 1.48-1.63) for late preterm delivery at 34 to 36 weeks
• 1.26 (95% CI 1.22-1.30) for early-term delivery at 37 to 38 weeks

The risk persisted out to 43 years of follow-up, although the magnitude dropped from a hazard ratio of 1.40 at 10 to 19 years after any preterm delivery to 1.20 at 20 to 29 years, and then to 1.12 at 30 to 43 years (all significant).

Studies have also linked preterm delivery — which affects nearly 11% of all births worldwide — to long-term risks of stroke, ischemic heart disease, and all-cause and cardiovascular disease (CVD) mortality, Crump and colleagues noted.

“These findings have important clinical implications,” they wrote. “Cardiovascular risk assessment in women should routinely include reproductive history that covers preterm delivery and other adverse pregnancy outcomes. This history should be a required element of electronic health records and linked with primary care to facilitate access by clinicians across patients’ life course.”

As an early warning sign, preterm delivery should trigger efforts to reduce other modifiable risk factors, like obesity, diet, alcohol overuse, smoking, and physical inactivity, and possibly ambulatory blood pressure monitoring too, they argued.

“These interventions should be implemented soon after preterm delivery, followed by long-term clinical monitoring for hypertension and other CVD risk factors,” they added. “Our findings also underscore the importance of public health strategies to help prevent preterm delivery, including better access to high-quality preconception and prenatal care, especially in the U.S. and other populations with a high prevalence of preterm birth.”

The findings were more suggestive that preterm delivery modulates the pathophysiologic mechanisms that lead to CVD, rather than by contributing directly to CVD, Crump and colleagues noted.

“Recent evidence suggests that preterm delivery may be a key event that triggers endothelial-specific inflammation that is undetectable before pregnancy,” they wrote. “The resulting endothelial dysfunction is associated with functional changes in the microvasculature, including impaired ability to release endothelium-derived relaxing factors, leading to increased constrictive tone.”

The study included all 2,195,989 women in the Swedish Medical Birth Register with a singleton delivery from 1973 through 2015 who were followed for new-onset chronic hypertension through administrative data from primary care, specialty outpatient, and inpatient visits. Of the 16.0% who were diagnosed with hypertension, mean age was 55.4 at development.

The associations were seen both for spontaneous and medically indicated delivery and were greater with recurrent preterm delivery.

“These findings were not explained by shared determinants of preterm delivery and hypertension within families,” the researchers noted.

Limitations included lack of detailed clinical records needed to verify hypertension diagnoses and use of last menstrual period rather than ultrasonography in the first part of the study period, which might have contributed to a slight conservative bias to the risk estimates. Also, the mean blood pressure threshold for hypertension was 140/90 mm Hg or receiving antihypertensive therapy, although newer guidelines have lower cutoffs.

“A priority for future research is to extend these findings to racial and ethnic subgroups that are at highest risk of preterm delivery and hypertension,” Crump’s group noted. “Additional follow-up will be needed to examine these associations in older adulthood when hypertension increasingly and disproportionately affects women.”