Hematologic Vulnerability in Gestational Hypertension: Platelet-Defined Severity Phenotypes and Maternal Outcomes

Gestational hypertension (GH) is commonly managed using blood pressure thresholds that may not fully reflect underlying biologic severity. Thrombocytopenia may identify higher-risk phenotypes within GH prior to overt clinical deterioration. To examine whether platelet-defined severity phenotypes are associated with adverse maternal outcomes among individuals with GH. A retrospective cohort study was conducted using electronic health record data from a large urban academic medical center between 2020 and 2024. The sample included pregnant individuals (n = 300) aged 18-49 years diagnosed with GH (ICD-10 O13.x), excluding chronic hypertension, preeclampsia, HELLP syndrome, multiple gestation, or fetal anomalies. Participants were stratified by platelet count as thrombocytopenia (<150 × 10⁹/L) or normal (≥150 × 10⁹/L). The primary outcome was maternal intensive care unit (ICU) admission during delivery hospitalization or the postpartum period. Secondary outcomes included magnesium sulfate administration, cesarean delivery, and preterm birth. Multivariable logistic regression evaluated predictors of ICU admission. Sensitivity analyses modeled platelet count as a continuous variable. Thrombocytopenia was present in 10.3% of the cohort. Blood pressure measures and unadjusted rates of ICU admission and secondary maternal outcomes did not differ significantly between platelet groups. However, thrombocytopenia independently predicted ICU admission after adjustment for demographic and clinical factors (aOR 3.89, 95% CI 1.19-12.70; p = .024). Platelet count demonstrated a dose-response relationship, with each 25 × 10⁹/L increase associated with a 17% reduction in ICU admission odds (aOR 0.83, 95% CI 0.73-0.94; p = .005). Platelet-defined phenotypes identify a biologically vulnerable subgroup within GH independent of blood pressure.