Preterm Delivery Associated with 1.6-Fold Increase in Risk of Hypertension Later in Life

Casey Crump, MD, PhD

An analysis of data from more than 2.1 million mothers suggests preterm delivery was associated with a 1.6-fold increase in risk of new-onset chronic hypertension.

An analysis of women with a singleton delivery in Sweden from 1973 through 2015, results of the study provide insight into the apparent increase of hypertension associated with preterm delivery in this patient population and also stratified according to weeks of gestation at delivery.

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

With an interest in further investigating associations of preterm delivery with long-term cardiometabolic disorders, a trio of clinicians from Icahn School of Medicine at Mount Sinai led by Casey Crump designed the current study as a national cohort study leveraging data from the Swedish Medical Birth Register. Using the register, which contains prenatal and birth information for deliveries in Sweden dating back to 1973, investigators sought to identify all singleton deliveries occurring from 1973-2015 for inclusion in their analysis.

Investigators noted singleton deliveries were selected to improve internal comparability and women with preexisting hypertension were excluded from the analysis. In total, 2,195,989 women with 4,308,286 deliveries were identified for inclusion. Of these, 351,189 (16.0%) went on to be diagnosed with hypertension during the follow-up period, which included 46.1 million person-years of follow-up.

The primary outcome of interest for the study was new-onset chronic hypertension, which was identified from primary care, specialty outpatient, and inpatient diagnoses using administrative data. Investigators noted plans to use Cox proportional hazards regression adjusted for preeclampsia, other hypertensive disorders of pregnancy, and other maternal factors to determine hazard ratios. Additionally, cosibling analyses were used to assess for potential confounding by shared familial factors.

Upon analysis, preterm delivery was associated with an increased risk for diagnosis of hypertension was observed within 10 years of delivery. Further analysis indicated this risk was greatest among those giving birth at 22-27 weeks (aHR, 2.23 [95% CI, 1.98-2.52]) of gestation followed by those giving birth at 28-33 weeks (aHR, 1.85 [95% CI, 1.74-1.97]), 34-36 weeks (aHR, 1.55 [95% CI, 1.48-1.63]), and 37-38 weeks (aHR, 1.26 [95% CI, 1.22-1.30]) compared with full-term delivery, which was defined as 39-41 weeks of gestation.

When examining risk beyond 10 years, results indicated the apparent risks decreased but remained significant at 10-19 years (aHR, 1.40 [95% CI, 1.36-1.44]), 20-29 years (aHR, 1.20 [95% CI, 1.18-1.23]), and 30-43 years (aHR, 1.12 [95% CI, 1.10-1.14]) after delivery. Additionally, cosibling analyses determined the findings were not explained by shared determinants of preterm delivery and hypertension within families.

“To our knowledge, this is the largest study to date of preterm delivery in relation to future risks of hypertension and the first to assess for potential confounding by shared familial factors using a cosibling design,” added investigators.

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