Study Population and Covariates

Table S1 describes the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD‐10‐CM) and International Classification of Diseases, Ninth Revision, Clinical Modification (ICD‐9‐CM) codes, which were used to identify delivery hospitalizations and patients previously diagnosed with PH. Individuals with age <18 years were excluded from our study. Variables including demographic characteristics (age, race and ethnicity, region, median income, insurance) and clinical history (hypertension, diabetes, hyperlipidemia, obesity, chronic heart failure, coronary artery disease, chronic kidney disease, and smoking status) were collected for analysis. Maternal complications at delivery were compared between pregnant patients with PH versus those without PH. The primary outcomes of interest were in‐hospital mortality, preeclampsia, eclampsia, PPCM, acute heart failure, acute coronary syndrome, ischemic and hemorrhagic stroke, pulmonary edema, cardiac arrhythmias, AKI, and VTE. Given small numbers of eclampsia, these cases were combined with preeclampsia. Acute heart failure was omitted due to overlap with pulmonary edema and PPCM. Since the NIS data are collected on a yearly basis, they can be utilized to analyze disease trends across duration using trend weights established by Healthcare Cost and Utilization Project.