Hypertensive complications of pregnancy contribute to the burden of maternal morbidity and subsequently have an impact on neonatal morbidity and mortality. Although codes from the International Classification of Diseases should delineate the specific subtypes of pregnancy-related hypertension, how diagnoses are applied and how these codes are used in clinical settings are largely unknown. This commentary discusses the implications of using administrative codes to identify women with preeclampsia syndromes, especially when used to define outcomes or exposures for etiologic research. Alemán