The Patient Classification System is a method used by nursing to characterize hospitalization units. The use of patient classification instruments allows estimating, quantifying and evaluating the demand for nursing care by groups of patients, categorizing them according to the need for nursing care by groups of patients, categorizing them according to need of care required by them, in a specific period of time. The applicability of a patient classification instrument is based on the forecast and management of human and material resources for assistance. Given the absence of a specific instrument for classifying pregnant and postpartum women in obstetric hospitalization wards, the objective of this project was to build and evaluate the evidence of validity of an instrument for classifying pregnant and postpartum women according to the demand for nursing care. This is a methodological study carried out in four stages: 1) elaboration of the instrument based on the bibliographic review; 2) application of the Delphi technique for content validation; 3) application of the instrument in a sample of 120 beds in an obstetric unit and analysis of the correlation with the Fugulin instrument. The instrument consisted of ten specific care indicators for pregnant and postpartum patients. A content validity index greater than 0.9 was obtained, requiring only one round of the Delphi technique. A Spearman coefficient of 0.64 was obtained between the instruments, indicating a strong correlation. The instrument built specifically for the assessment of pregnant and postpartum women showed evidence of content validity and convergent validity with a patient classification instrument widely used in the national territory. The specificity of the indicators related to the pregnancy and puerperal cycle can qualify the nursing assessment regarding the care demand of pregnant and puerperal women in the management practice of patient classification.