Aspirin for the Prevention of Preeclampsia in Women With Stage 1 Hypertension

In 2017, the American College of Cardiology (ACC) and the American Heart Association (AHA) changed the diagnostic criteria for hypertension in non-pregnant adults.1 The parameters for the diagnosis of stage 1 hypertension were revised from a systolic blood pressure (BP) of 140 to 130 mm Hg and a diastolic BP of 90 to 80 mm Hg.2 Stage 1 hypertension based on the new criteria is associated with an increased risk of preeclampsia compared to normal BP (15-16% vs. 5-7%).3, 4 However, the American College of Obstetricians and Gynecologists (ACOG) continues to diagnose chronic hypertension in pregnancy as a systolic BP above 140 mm Hg and a diastolic BP of 90 mm Hg since there are no data regarding prevention of preeclampsia in women with stage 1 hypertension.5

Preeclampsia is a multi-organ, progressive disorder characterized by the new onset of hypertension with proteinuria or end-organ dysfunction.6 Preeclampsia is a major cause of morbidity such as eclampsia, pulmonary edema, myocardial infarction, stroke, coagulopathy, and renal failure and a leading cause of iatrogenic preterm birth and maternal mortality.7 Preeclampsia is also an economic burden to the health care system. The mean combined maternal and infant medical care costs for women with preeclampsia are significantly higher than those of uncomplicated women ($41,790 vs. $13,187 in 2015 dollars) with the main cost drivers being infant health care costs due to prematurity.8

It is hypothesized that preeclampsia is caused by an imbalance in prostacyclin and thromboxane A2 (TXA2) resulting in vascular disturbances and coagulation defects. Low-dose aspirin (60-150 mg/day) irreversibly acetylates cyclooxygenase (COX)-1, which results in decreased platelet synthesis of TXA2 without affecting vascular wall production of prostacyclin.9. 10 However, it is likely that preeclampsia is a result of poor placentation. In this pilot study, we will examine the effect of low-dose aspirin on placental perfusion by using novel ultrasound tools (Superb Micro-Vascular Imaging [SMI], Shear Wave Elastography [SWE], intensity analysis [IA], and Attenuation Imaging [ATI]). Superb Micro-Vascular Imaging (SMI) is a novel Doppler technique designed to improve the visualization of microscopic vessels, through a new adaptive algorithm, which dramatically enhances microvascular flow and removes artifacts. Shear Wave Elastography (SWE) is a new noninvasive ultrasound-based technology for the evaluation of soft tissue stiffness. Intensity Analysis (IA) is a technique that analyzes tissue homogeneity. Attenuation Imagining (ATI) measures beam attenuation by quantifying an attenuation coefficient (AC db/cm/MHz). Our group has developed longitudinal nomograms on placental vasculature to include uterine and spiral arteries on the maternal side and fetal placental arterioles and umbilical artery on the fetal side.11 Furthermore, longitudinal nomograms related to placental tissue structure, including shear wave elastography has been developed.12

Although the precise mechanism is uncertain, low-dose aspirin has been used during pregnancy to prevent or delay the onset of preeclampsia for women at high-risk for preeclampsia.13 The 2017 Aspirin for Evidence-Based Preeclampsia Prevention trial compared 150 mg aspirin with placebo in women at high-risk of preeclampsia based on a first-trimester screening.14 They found a significant decrease in the rate of preterm preeclampsia less than 37 weeks of gestation (4.3% vs. 1.6%; P <0.01). Since this study used the screening algorithm including first-trimester serum markers and uterine artery Doppler, the generalizability of aspirin preeclampsia prevention in the U.S. women with stage 1 hypertension is limited.

Our long-term goal is to reduce preterm preeclampsia in women with stage 1 hypertension. We hypothesize that 1) spiral artery Pulsatility Index (PI) and Peak Systolic Velocity (PSV) and SWE is lower in women with stage 1 hypertension who receive low-dose aspirin 81 mg compared to those who do not receive low-dose aspirin; 2) Women with stage 1 hypertension who receive low-dose aspirin 81 mg have a lower rate of preterm preeclampsia compared to those who do not receive low-dose aspirin. To examine these hypotheses in a future, large randomized, controlled trial, our aims for this pilot study include the following:

Aim 1. To examine the change in placental vasculature and tissue elastography in women with stage 1 hypertension who receive low-dose aspirin 81 mg and those who do not receive low-dose aspirin.

Aim 2. To examine rates of preterm preeclampsia in women with stage 1 hypertension who receive low-dose aspirin 81 mg and those who do not receive low-dose aspirin.

Aim 3. To examine eligibility rate, recruitment rate, study compliance, and loss of follow-up rate. This information will be useful to assess feasibility of a future multicenter randomized controlled trial.

In summary, women with stage 1 hypertension are at an increased risk of preeclampsia. Low-dose aspirin may reduce the rate of preterm preeclampsia in women with stage 1 hypertension. In this pilot study, we will conduct an open label randomized controlled trial and obtain necessary information for a future multicenter randomized controlled trial.