Defining the risk profile of women with stage 1 hypertension: a time to event analysis

Abstract

Background: Chronic hypertension complicates up to 5% of pregnancies and is increasing in prevalence. Women with hypertension have increased risks of serious maternal morbidity and mortality in pregnancy, including the development of preeclampsia. In 2017, new guidelines reclassified blood pressure into the following 4 categories: normal (<120/<80 mm Hg), elevated (120-129/<80 mm Hg), stage 1 hypertension (130-139/80-89 mm Hg), and stage 2 hypertension (>140/>90 mm Hg). This new classification doubles the number of reproductive-aged women with hypertension. Furthermore, studies have demonstrated that women entering pregnancy with stage 1 hypertension have an increased risk of developing hypertensive disorders of pregnancy compared with their normotensive counterparts, but the time course to the development of hypertensive disorders of pregnancy in these women remains uncertain.

Objective: We sought to evaluate the risk of developing a hypertensive disorder of pregnancy and the time to the development of these disorders in women with stage 1 hypertension vs both normotensive women and those with stage 2 hypertension.

Study design: This was a retrospective cohort study of all patients from a single tertiary care center with singleton gestations from 2014 to 2016. Patients at prenatal visits before 20 weeks of gestation were classified into 3 blood pressure groups: normotensive (<130/80 mm Hg), stage 1 hypertension (130-139/80-89 mm Hg), or stage 2 hypertension (≥140/90 or a history of chronic hypertension). The primary outcome, time to the development of a hypertensive disorder of pregnancy, was compared among groups using Kaplan-Meier curves and the log-rank test. Cox proportional-hazards models were used to adjust for age, race and ethnicity, pregestational diabetes mellitus, and body mass index. In addition, multiple secondary obstetrical, maternal, and neonatal outcomes were assessed.

Results: Of the 3000 women in our cohort, 2370 (79.0%) were categorized in the normotensive group, 315 (10.5%) were categorized in the stage 1 hypertension group, and 315 (10.5%) were categorized in the stage 2 hypertension group. The gestational age at diagnosis was significantly earlier in gestation among blood pressure groups (normotensive [38.7 (37.0-39.7)] vs stage 1 hypertension [38.0 (36.4-39.4)] vs stage 2 hypertension [36.4 (33.7-37.8)]; P<.001). When the analysis was restricted to only those patients diagnosed with preeclampsia with severe features, the same findings were observed. Women with stage 1 hypertension exhibited a 2-fold increased risk of developing hypertensive disorders of pregnancy compared with normotensive women. Compared with women with stage 2 hypertension, women with stage 1 hypertension exhibited a milder phenotype of hypertensive disorders of pregnancy and exhibited significantly less risk of maternal and neonatal morbidities.

Conclusion: Women with stage 1 hypertension are at increased risk of developing hypertensive disorders of pregnancy at earlier gestational ages compared with normotensive women; however, their development of a hypertensive disorder of pregnancy is skewed toward milder diseases compared with women with stage 2 hypertension. These new insights into the graded risk profile of obstetrical hypertensive diseases associated with new blood pressure categories can better inform our antepartum counseling and monitoring and surveillance plans near term and in the postpartum period.

Keywords: adverse pregnancy outcomes; chronic hypertension; gestational hypertension; maternal morbidity; neonatal outcomes; preeclampsia; small for gestational age.