Importance: Preterm delivery has been associated with future cardiometabolic disorders in women. However, the long-term risks of chronic hypertension associated with preterm delivery and whether such risks are attributable to familial confounding are unclear. Such knowledge is needed to improve long-term risk assessment, clinical monitoring, and cardiovascular prevention strategies in women.
Objective: To examine the long-term risks of chronic hypertension associated with preterm delivery in a large population-based cohort of women.
Design, setting, and participants: This national cohort study assessed all 2 195 989 women in Sweden with a singleton delivery from January 1, 1973, to December 31, 2015. Data analyses were conducted from March 8, 2021, to August 20, 2021.
Exposures: Pregnancy duration identified from nationwide birth records.
Main outcomes and measures: New-onset chronic hypertension identified from primary care, specialty outpatient, and inpatient diagnoses using administrative data. Cox proportional hazards regression was used to compute hazard ratios (HRs) while adjusting for preeclampsia, other hypertensive disorders of pregnancy, and other maternal factors. Cosibling analyses were assessed for potential confounding by shared familial (genetic and/or environmental) factors.
Results: In 46.1 million person-years of follow-up, 351 189 of 2 195 989 women (16.0%) were diagnosed with hypertension (mean [SD] age, 55.4 [9.9] years). Within 10 years after delivery, the adjusted HR for hypertension associated with preterm delivery (gestational age <37 weeks) was 1.67 (95% CI, 1.61-1.74) and when further stratified was 2.23 (95% CI, 1.98-2.52) for extremely preterm (22-27 weeks of gestation), 1.85 (95% CI, 1.74-1.97) for moderately preterm (28-33 weeks of gestation), 1.55 (95% CI, 1.48-1.63) for late preterm (34-36 weeks of gestation), and 1.26 (95% CI, 1.22-1.30) for early-term (37-38 weeks of gestation) compared with full-term (39-41 weeks of gestation) delivery. These risks decreased but remained significantly elevated at 10 to 19 years (preterm vs full-term delivery: adjusted HR, 1.40; 95% CI, 1.36-1.44), 20 to 29 years (preterm vs full-term delivery: adjusted HR, 1.20; 95% CI, 1.18-1.23), and 30 to 43 years (preterm vs full-term delivery: adjusted HR, 95% CI, 1.12; 1.10-1.14) after delivery. These findings were not explained by shared determinants of preterm delivery and hypertension within families.
Conclusions and relevance: In this large national cohort study, preterm delivery was associated with significantly higher future risks of chronic hypertension. These associations remained elevated at least 40 years later and were largely independent of other maternal and shared familial factors. Preterm delivery should be recognized as a lifelong risk factor for hypertension in women.