De Novo Postpartum Hypertension: is Pregnancy a Stress Test or Risk Factor?

In this edition of Hypertension, Parker et al.¹ present intriguing data on the risk of de novo postpartum hypertension in the year following pregnancy among patients without a prior diagnosis of chronic or pregnancy-related hypertension. They performed an observational cohort study of racially diverse patients receiving prenatal care and delivering at Boston Medical Center, Boston, United States (US) from 2016–2018 to estimate the incidence of de novo postpartum hypertension through the first year postpartum. Two blood pressure (BP) readings with systolic BP ≥140 mmHg or diastolic BP≥90 mmHg ≥48 hours following delivery were required for de novo postpartum hypertension diagnosis. The observed rate of de novo postpartum hypertension in the total cohort was 12.1% (n = 298 / 2,465); the rate was as high as one in three for patients with advanced maternal age (≥35 years), tobacco use history and cesarean delivery. The authors conclude that certain patient characteristics (body mass index ≥ 30kg/m², current tobacco use, substance use, diabetes and cesarean delivery) may help prenatally identify pregnant people at risk of developing de novo postpartum hypertension.¹

A concern exists whether the authors are capturing patients with a missed pre-pregnancy diagnosis of chronic hypertension. Systemic vascular resistance decreases in the first trimester of pregnancy and BPs may be up to 30% lower than baseline in the second trimester.² However, when the study population was restricted to the 1,392 patients who entered prenatal care at ≤13 weeks’ gestation, the de novo postpartum hypertension rate was similar at 13.3%, strengthening the credibility of the authors’ findings.

Figure 1 depicts rates of hypertensive disorders across various stages of a reproductive-aged female. Approximately 8% of reproductive-aged females have chronic hypertension, and 2–8% of pregnancies are complicated by gestational hypertension or preeclampsia.^3,4 Excluding de novo postpartum hypertension, nearly one in 10 pregnancies is complicated by hypertension. Once de novo postpartum hypertension is included, up to one in five pregnant people experience a hypertensive disorder. Pregnancy associated hypertension should thus be viewed as a top public health priority.

Figure 1:

Frequency of hypertensive disorders across the pregnancy spectrum

Footnote: HTN: Hypertension

A prior randomized trial in non-pregnant adults without diabetes comparing intensive to standard BP control (systolic BP ≤120 vs ≤140 mmHg) found a lower incidence of an adverse cardiovascular composite in participants assigned to intensive BP treatment (HR 0.75, 95%CI 0.64–0.89).⁵ Further, the results of the recent Chronic Hypertension and Pregnancy trial showed an 18% reduced risk (RR 0.82, 95% CI 0.74–0.92) of a composite of severe preeclampsia, preterm delivery <35weeks, placental abruption or fetal or neonatal death, following treatment of mild chronic hypertension to BPs <140/90mmHg in pregnancy.⁶ Maternal follow up from this cohort is ongoing. Taken together with the findings from Parker et al., the first year following delivery may provide a window of opportunity for lifestyle interventions, and when applicable, antihypertensive initiation, to attain lower BP in a group at high-risk of developing chronic hypertension.

The US Preventive Services Taskforce currently recommends office blood pressure measurements for adults ≥18 years at routine preventive yearly visits. Postpartum de novo hypertension screening is widely available, associated with minimal risk and can identify early chronic hypertension which has been shown to reduce cardiovascular risk. Screening strategies that can overcome numerous social determinants of health barriers are critical. In the United States, only 23 states have implemented expanded Medicaid coverage for up to one year postpartum.⁷ Nationally, Medicaid remains the largest healthcare insurer (42%) in pregnancy and loss of postpartum insurance coverage is often an insurmountable barrier to preventive healthcare.^8,9,10 Since more than one in five participants (22.5%) in the study by Parker et al. developed de novo postpartum hypertension after six weeks postpartum, insurance coverage expansion may improve postpartum identification and treatment of patients with de novo postpartum hypertension. Further, Black patients in this cohort had the highest risk of de novo postpartum hypertension at 14%, highlighting opportunities to reduce marked racial disparities in the year after delivery.

Importantly, the threshold for the diagnosis of de novo postpartum hypertension used in the study by Parker et al. was systolic or diastolic BP ≥140/90mmHg, respectively. In 2017 the ACC/AHA recommended BP ≥130/80 mmHg for the diagnosis of stage 1 hypertension, which has been estimated to increase the prevalence of chronic hypertension in pregnancy from 4.2% to 25.0%, in one study.¹¹ If applied to the study by Parker et al., the prevalence of de novo postpartum hypertension would likely be even higher, broadening the number of people who may benefit from risk reducing interventions. Although prospective studies are needed to investigate the prevalence of de novo postpartum hypertension in other populations, these findings challenge the traditional views of pregnancy only as a stress-test that unmasks underlying susceptibility to hypertension.¹² The increased risk of chronic hypertension and cardiovascular morbidity following a hypertensive disorder of pregnancy have been well described.¹³ Further, it is accepted that pregnancy-associated factors – such as gestational weight gain, a risk factor for obesity – may contribute to the future development of chronic hypertension. However, elucidation of the role of pregnancy-related cardiovascular remodeling in the causal pathway to chronic hypertension is needed. The findings by Parker et al. turns the spotlight on the significant burden of hypertension across the reproductive spectrum, highlight the need for policy and interventions to improve cardiovascular health and beg the question: Is pregnancy a stress test, a risk factor or both?