Beyond the Diastolic Threshold: Isolated Severe Systolic Hypertension as a Potent Predictor of Maternal Risk

Highlights

Isolated severe systolic hypertension (ISSH), defined as a systolic blood pressure (SBP) ≥160 mmHg with a diastolic blood pressure (DBP) <110 mmHg, is a significant and independent risk factor for severe maternal morbidity.

In a secondary analysis of the APEX cohort, patients with SBP between 160-179 mmHg faced a 2.8-fold increase in adverse maternal outcomes, while those with SBP ≥180 mmHg faced a nearly 4-fold increase compared to patients with mild hypertension.

The increased risk is primarily driven by life-threatening complications, including pulmonary edema and acute renal dysfunction (elevated creatinine).

A clear linear trend exists between the severity of isolated systolic elevations and the probability of adverse outcomes, suggesting that systolic pressure should be a primary focus of clinical management.

The Evolution of Blood Pressure Monitoring in Obstetrics

For decades, obstetric guidelines and clinical practice have placed a heavy emphasis on diastolic blood pressure as the primary indicator of hypertensive severity and the threshold for pharmacological intervention. This historical focus was rooted in early studies suggesting that diastolic pressure more accurately reflected peripheral vascular resistance and the risk of eclampsia. However, data from non-pregnant cardiovascular research has long established that systolic blood pressure is often a superior predictor of end-organ damage, particularly stroke and heart failure, in the general population.

In recent years, the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) have updated their recommendations to include systolic thresholds (≥160 mmHg) as a trigger for urgent antihypertensive therapy. Despite these changes, there has been limited evidence specifically isolating the prognostic significance of severe systolic hypertension when diastolic values remain below the traditional 110 mmHg danger zone. This study aims to fill that gap by evaluating the independent risks associated with isolated severe systolic hypertension (ISSH) during the critical window of delivery admission.

Study Design: The APEX Cohort Analysis

The findings are derived from a secondary analysis of the Assessment of Perinatal Excellence (APEX) cohort, a massive multicenter study involving 115,502 patients across 25 hospitals participating in the NICHD Maternal-Fetal Medicine Units Network between 2008 and 2011. This robust dataset provides the statistical power necessary to detect rare but severe maternal complications.

The study focused on patients who exhibited elevated blood pressure during their delivery admission (from admission to discharge). Elevated blood pressure was defined by at least two readings taken at least 30 minutes apart. The researchers categorized patients into three primary groups based on their peak blood pressure values:

1. Reference Group (Mild Hypertension)

Patients with SBP 140-159 mmHg and/or DBP 90-109 mmHg.

2. Intermediate ISSH Group

Patients with SBP 160-179 mmHg and DBP <110 mmHg.

3. Severe ISSH Group

Patients with SBP ≥180 mmHg and DBP <110 mmHg.

The primary outcome was a composite of severe adverse maternal events, including hypertensive stroke, pulmonary edema, renal failure (creatinine ≥1.5 mg/dl), disseminated intravascular coagulation (DIC), cardiopulmonary arrest, and death. To ensure the results were truly representative of the impact of systolic pressure, the models were adjusted for maternal age, BMI, chronic hypertension, diabetes, preterm birth, and delivery method.

Dissecting the Results: A Linear Escalation of Risk

The results of the analysis reveal a stark, stepwise correlation between rising systolic pressure and maternal danger. Of the total cohort, 32,277 patients met the criteria for mild hypertension, 3,790 had ISSH 160-179, and 2,178 had ISSH ≥180 mmHg.

The data showed that as systolic pressure climbed, so did the adjusted relative risk (aRR) of the composite adverse outcome:

• SBP 160-179 mmHg: aRR 2.8 (95% CI 2.1-3.6)
• SBP ≥180 mmHg: aRR 3.8 (95% CI 2.9-5.1)

This nearly four-fold increase in risk for the highest systolic group is a critical finding. When the researchers stratified the cohort into even smaller systolic intervals, the linear trend remained consistent, reinforcing the idea that there is no “safe” level of severe systolic elevation, even if the diastolic pressure appears manageable.

The primary drivers of the composite outcome were pulmonary edema and elevated creatinine. Additionally, patients in the ISSH categories were significantly more likely to experience eclampsia, HELLP syndrome (hemolysis, elevated liver enzymes, and low platelets), and required admission to the intensive care unit (ICU).

Pathophysiological Mechanisms and Clinical Implications

Why does isolated systolic hypertension carry such high risk? From a physiological perspective, systolic blood pressure represents the peak force exerted against arterial walls during ventricular contraction. High systolic pressure significantly increases cardiac afterload and wall stress, which can lead to left ventricular dysfunction and the subsequent development of pulmonary edema—one of the leading causes of maternal death in hypertensive disorders of pregnancy. Furthermore, the high pressure can cause endothelial injury in the delicate microvasculature of the kidneys, leading to the renal impairment observed in the study.

For clinicians, these findings underscore the necessity of treating severe systolic hypertension with the same urgency as severe diastolic hypertension. The traditional comfort taken in a “normal” or “mildly elevated” diastolic reading (e.g., 165/95 mmHg) is clinically unjustified. This study suggests that the systolic component is a potent, independent driver of vascular and organ-system failure.

Expert Commentary and Study Limitations

The APEX analysis provides some of the strongest evidence to date for the prognostic value of SBP in the peripartum period. However, as with any secondary analysis, there are limitations. The study lacked granular data on the specific antihypertensive medications administered and the exact timing of those treatments relative to the blood pressure peaks. It is possible that some patients in the ISSH groups received treatment that mitigated even worse outcomes, meaning the natural risk of untreated ISSH might be even higher than reported.

Furthermore, because the data was collected between 2008 and 2011, clinical practices regarding systolic targets have evolved. However, the biological relationship between SBP and end-organ damage remains constant, making these findings highly relevant to modern obstetric care.

Conclusion: A Call for Heightened Vigilance

The study by Bart et al. clarifies that isolated severe systolic hypertension is not a benign variant of pregnancy-related hypertensive disorders. It is a high-risk state characterized by a stepwise increase in maternal morbidity. Healthcare providers should maintain a high index of suspicion and adhere strictly to protocols for the rapid treatment of systolic blood pressure ≥160 mmHg, regardless of the diastolic value. By focusing on the systolic component, clinicians can better identify at-risk patients and intervene early to prevent complications such as pulmonary edema and renal failure, ultimately improving maternal safety during the delivery admission.

Reference:

Bart Y, Mendez-Figueroa H, Amro FH, Zaki Moustafa AS, Blackwell SC, Sibai BM. Isolated Severe Systolic Hypertension With Diastolic <110 mmHg During Delivery Admission and Maternal Outcomes: A Secondary Analysis of the APEX Cohort. Am J Obstet Gynecol. 2025 Dec 18:S0002-9378(25)00942-1. doi: 10.1016/j.ajog.2025.12.045 . Epub ahead of print. PMID: 41421751.