Incidence and Long-Term Outcomes of Hypertensive Disorders of Pregnancy

Abstract

Background: Hypertensive disorders of pregnancy (HDP) are associated with increased risks for cardiovascular disease later in life. The HDP incidence is commonly assessed using diagnostic codes, which are not reliable; and typically are expressed per-pregnancy, which may underestimate the number of women with an HDP history after their reproductive years.

Objectives: This study sought to determine the incidence of HDP expressed as both per-pregnancy and per-woman, and to establish their associations with future chronic conditions and multimorbidity, a measure of accelerated aging, in a population-based cohort study.

Methods: Using the Rochester Epidemiology Project medical record-linkage system, the authors identified residents of Olmsted County, Minnesota, who delivered between 1976 and 1982. The authors classified pregnancies into normotensive, gestational hypertension, pre-eclampsia, eclampsia, pre-eclampsia superimposed on chronic hypertension, and chronic hypertension using a validated electronic algorithm, and calculated the incidence of HDP both per-pregnancy and per-woman. The risk of chronic conditions between women with versus those without a history of HDP (age and parity 1:2 matched) was quantified using the hazard ratio and corresponding 95% confidence interval estimated from a Cox model.

Results: Among 9,862 pregnancies, we identified 719 (7.3%) with HDP and 324 (3.3%) with pre-eclampsia. The incidence of HDP and pre-eclampsia doubled when assessed on a per-woman basis: 15.3% (281 of 1,839) and 7.5% (138 of 1,839), respectively. Women with a history of HDP were at increased risk for subsequent diagnoses of stroke (hazard ratio [HR]: 2.27; 95% confidence interval [CI]: 1.37 to 3.76), coronary artery disease (HR: 1.89; 95% CI: 1.26 to 2.82), cardiac arrhythmias (HR: 1.62; 95% CI: 1.28 to 2.05), chronic kidney disease (HR: 2.41; 95% CI: 1.54 to 3.78), and multimorbidity (HR: 1.25; 95% CI: 1.15 to 1.35).

Conclusions: The HDP population-based incidence expressed per-pregnancy underestimates the number of women affected by this condition during their reproductive years. A history of HDP confers significant increase in risks for future chronic conditions and multimorbidity.

Keywords: cardiovascular disease; hypertensive disorders of pregnancy; incidence; multimorbidity.

Figure 1.. Inclusion criteria and study cohorts.

Using a population-based study, two cohorts of women were identified with the goal to compute and compare the HDP incidence per-pregnancy versus the HDP incidence per woman. * The cut-off of 46 years was chosen as this was the oldest age at which a pregnancy was documented in this cohort. **A pregnancy was classified as having sufficient information to determine HDP status if there was at least one blood pressure measurement from a prenatal visit and at least one blood pressure measurement from admission for delivery. † St. Sauver JL, Grossardt BR, Yawn BP, Melton LJr, Rocca WA. Use of a medical records linkage system to enumerate a dynamic population over time: The Rochester Epidemiology Project. Am J Epidemiol 2011;173:1059–68. REP: Rochester Epidemiology Project

Figure 2.. Age-specific per-pregnancy incidence of hypertensive disorders of pregnancy among 9,862 pregnancies during 1976–1982 for residents of Olmsted County, Minnesota.

The per-pregnancy incidence of preeclampsia with respect to age was U-shaped, such that the youngest women (i.e., <20 years and 20–24 years) and those ages ≥35 years had the highest incidence. HTN: hypertension

Figure 3.. Cumulative incidence curves for cardiovascular and metabolic conditions in women with HDP compared with 1:2 age- and parity-matched referent women.

The reported HRs and corresponding 95% CIs and p-values were estimated from Cox models adjusted for education, smoking, and obesity. Age was used as the time scale. Women with HDP compared to referent women demonstrated increased risks of CVD risk factors and events. HDP: hypertensive disorders of pregnancy. HR: hazard ratio. CI: confidence intervals.

Central Illustration:. Hypertension in pregnancy: incidence per-pregnancy and per-woman, outcomes and multimorbidity later in life.

Conventional per pregnancy incidence values underestimate the number of women experiencing HDP by half. Women with a history of HDP compared with referent women, have increased risks for developing multimorbidity, CVD risk factors and events earlier in life.