Preterm delivery and mother’s long-term risk of hypertension

The cohort study of more than 2 million women in Sweden accounted for preeclampsia, other hypertensive disorders of pregnancy, and additional maternal factors.

The risk of hypertension decreased, but remained significantly elevated 40 years after delivery, but was largely independent of other maternal and shared familial factors.

“These results suggest that preterm delivery is a lifelong risk factor for hypertension in women,” wrote the authors.

The national cohort study evaluated all 2,195,989 women in Sweden with a singleton delivery between January 1973 and December 2015.

New-onset chronic hypertension was identified from primary care, specialty outpatient and inpatient diagnoses via administrative data.

In 46.1 million person-years of follow-up, 16.0% of women were diagnosed with hypertension at a mean age of 55.4 years.

Within 10 years after delivery, the adjusted hazard ratio (aHR) for hypertension linked to preterm delivery (gestational age < 37 weeks) was 1.67; 95% confidence interval (CI): 1.61 to 1.74.

Compared to full-term delivery (39 to 41 weeks of gestation), the aHR was 2.23 for extremely preterm (22 to 27 weeks of gestation); 1.85 for moderately preterm (28 to 33 weeks of gestation); 1.55 for late preterm (34 to 36 weeks of gestation); and 1.26 for early term (37 to 38 weeks of gestation).

These risks decreased but remained significantly elevated at 10 to 19 years after delivery: aHR of 1.40 for preterm vs. full-term delivery.

Further out, the aHR was 1.20 for 20 to 29 years and 1.12 for 30 to 43 years after delivery when comparing preterm to full-term delivery.

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

Women with recurrent preterm delivery had further increases in risk. For instance, for each additional preterm delivery at less than 10 years of follow-up, the aHR was 1.51; which decreased to 1.28 at 10 to 19 years of follow-up, 1.12 at 20 to 29 years of follow-up, and 1.10 at 30 to 43 years of follow-up (P < .001 for each).

Both spontaneous and medically indicated delivery at preterm or early term were connected to increased risks of chronic hypertension versus full-term delivery: aHR of 1.25 (P < .001) and 1.46 P < .001), respectively.

Medically indicated preterm delivery that was specifically related to preeclampsia or other hypertensive disorders of pregnancy had an aHR of 1.67; 95% CI: 1.62 to 1.73 (P < .001).

Likewise, chronic hypertension from preterm delivery for other indications, primarily diabetes, had an aHR of 1.41; 95% CI: 1.35 to 1.47; (P < .001).

The study’s findings are consistent with previously reported links between preterm delivery and long-term risks of stroke, ischemic heart disease, and all-cause and cardiovascular disease mortality, according to the authors.

“Preterm delivery should now be recognized as a risk factor for hypertension across the life course,” they wrote.

The authors also noted that women with a history of preterm delivery require early preventive assessment and long-term risk reduction and monitoring for hypertension.

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Reference

Crump C, Sundquist J, Sundquist K. Preterm delivery and long-term risk of hypertension in women. JAMA Cardiol. Published online October 13, 2021. doi:10.1001/jamacardio.2021.4127