Preterm Delivery Associated with Risk of Chronic Hypertension in Women

Since the long term risks of chronic hypertension associated with preterm delivery are still unclear, a new study aimed to improve long-term risk assessment and cardiovascular prevention strategies in women.

Led by Casey Crump, MD, PhD, Department of Family Medicine and Community Health, Icahn School of Medicine at Mount Sinai, investigators performed a national cohort study of 2 million women in Sweden, to examine the risk of chronic hypertension associated with preterm delivery.

The team of investigators observed preterm delivery had an association with significantly higher future risks of chronic hypertension, which remained elevated at least 40 years later, independent of other maternal and familial factors.

Methods

Data was collected from the Swedish Medical Birth Register, containing all prenatal and birth information for nearly all deliveries in Sweden since 1973.

Investigators identified 4,331,668 singleton deliveries in 2,203,746 women from January 1973 - December 2015. They noted singleton deliveries were chosen to improve internal comparability due to higher prevalence of preterm delivery.

From this number, a total of 2,195,989 women (99.6%) with 4,308,286 deliveries remained for inclusion in the study. Data analyses were conducted from March - August 2021.

Additionally, pregnancy duration was examined as a continuous variable or categorical variable with 6 groups based on the number of completed weeks. These included extremely preterm (22 - 27 weeks of gestation), moderately preterm (28 - 33 weeks), late preterm (34 - 36 weeks), early-term (37 - 38 weeks), full-term (39 - 41 weeks), and postterm (≥42 weeks).

The main outcome was defined as a new-onset chronic hypertension diagnosis that occurred more than 12 weeks postpartum in order to distinguish chronic from gestational hypertension.

In the analysis, investigators used cox proportional hazards regressions to calculate hazard ratios (HRs), adjusting for preeclampsia and other hypertensive disorders of pregnancy.

What are the findings?

Out of a total of 46.1 million person-years of follow-up, data show 351,189 of 2,195,989 women (16.0%) were diagnosed with hypertension, with a mean age of 55.4 years.

Investigators identified women who delivered preterm were more likely to be younger than 20 years, have a low educational level, be unemployed, smoke, or have high prenatal BMI, preeclampsia, or other hypertensive disorders of pregnancy.

Further, within 10 years after delivery, the adjusted HR for hypertension associated with preterm delivery was 1.67 (95% CI, 1.61 - 1.74).

Then, when further stratified, the adjusted HR was 2.23 (95% CI, 1.98 - 2.52) for extremely preterm, 1.85 (95% CI, 1.74 - 1.97) for moderately preterm, 1.55 (95% CI, 1.48 - 1.63) for late preterm, and 1.26 (95% CI, 1.22 - 1.30) for early-term, in comparison to full-term delivery.

It showed a mean 7% lower risk with each additional week of pregnancy (adjusted HR, 0.93; 95% CI, 0.93 - 0.94).

A decrease was seen, but remained significantly elevated at 10 - 19 years (preterm versus full-term delivery: adjusted HR, 1.40, 95% CI, 1.36 - 1.44), 20 - 29 years (preterm versus full-term delivery: adjusted HR, 1.20, 95% CI, 1.18 - 1.23), and 30 - 43 years (preterm versus full-term delivery: adjusted HR, 1.12 95% CI, 1.10 - 1.14) after delivery.

However, investigators noted these had no explanation due to shared determinants of preterm delivery and hypertension within families.

What are the takeaways?

“Preterm delivery should now be recognized as a risk factor for hypertension across the life course,” investigators wrote. “Women with a history of preterm delivery need early preventive evaluation and long-term risk reduction and monitoring for hypertension.”

The study, “Preterm Delivery and Long-term Risk of Hypertension in Women,” was published in JAMA Cardiology.