Co-existing chronic hypertension and hypertensive disorders of pregnancy and associated adverse pregnancy outcomes

Objective: Chronic hypertension (CHTN) causes vascular damage and resistance in the pregnant person and malperfusion in the placenta which may worsen the endothelial dysfunction of hypertensive disorders of pregnancy (HDP). These conditions frequently co-exist. A cumulative effect has been inconsistently demonstrated in prior studies, and it is unclear how co-existing hypertensive conditions affect pregnancy outcomes. We sought to examine maternal and neonatal outcomes in pregnancies affected by co-existing CHTN and HDP and compare these outcomes to those of pregnancies which were unaffected or affected by either condition alone. Methods: This is a retrospective cohort study of singleton deliveries at a single institution 1 October 2013 to 1 October 2021. Data were extracted from the electronic medical record using standardized definitions and billing and diagnosis codes. Pregnant people with no evidence of hypertensive condition were compared to those with CHTN only, HDP only, and co-existing CHTN and HDP. Demographics, baseline clinical data, and use of aspirin or antihypertensive medications were assessed. Maternal outcomes included cesarean delivery, critical range blood pressure, intensive care unit (ICU) admission, and death. Neonatal outcomes included preterm birth <37 weeks' gestation, small for gestational age (SGA) birthweight, ICU admission, and a morbidity composite. Bivariate tests of association were performed using Chi-square test. Crude and adjusted odds ratios (aORs) were calculated using logistic regression for three maternal and four neonatal outcomes. Descriptive statistics and multivariable analyses were performed. Results: Of 40,840 eligible people, 1451 (3.6%) had CHTN only; 5213 (12.8%) had HDP only; and 1890 (4.6%) had co-existing CHTN and HDP. Though odds of adverse maternal and neonatal outcomes were significantly increased for all hypertensive groups relative to the unaffected referent group, co-existing CHTN and HDP had the highest odds of cesarean delivery (aOR 1.60; 95% confidence interval (CI) 1.45-1.77), critical blood pressure (OR 41.54; 95% CI 35.96-47.99), maternal ICU admission or death (aOR 3.52; 95% CI 2.65-4.67), preterm birth (aOR 2.76; 95% CI 2.41-3.16), and SGA birthweight (aOR 1.61; 95% CI 1.39-1.87). Conclusions: Hypertensive disorders of pregnancy in the setting of CHTN are associated with the highest odds of serious consequences on the pregnant person and neonate independent of maternal comorbidities and prematurity. Antihypertensive medication use lowers the odds of some adverse outcomes. Patients should be informed of heightened risks, but optimal management remains unclear.