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Publisher Summary The increasing demands of the fetus as well as biologic differences between the fetus and the mother significantly affect the management of a patient during pregnancy. The chapter discusses several obstetric considerations including physiologic adaptations to pregnancy, issues related to the assessment of obstetric hemorrhage, and the need for maternal transfusion. It also discusses the diagnosis and treatment of fetomaternal hemorrhage (FMH) and its contribution to the hemolytic disease of the fetus and the newborn, with emphasis on rhesus (Rh) isoimmunization. The physiologic changes that occur during pregnancy are designed to protect the patient from the significant amount of blood loss caused by delivery. After delivery, mothers are screened for FMH by\ the erythrocyte rosette test. The rosette test identifies Rh(D)-positive fetal cells in the maternal circulation. The maternal red blood cell (RBC) sample is first incubated with human anti-D antibody, and then indicator Rh(D)-positive cells are added. The indicator cells form agglutinates (rosettes) around the antibody-bound Rh(D)-positive fetal cells if present. If the rosette test is positive, a Kleihauer–Betke test is used to quantitate the number of fetal cells in the maternal circulation. This technique relies on differences between fetal and adult hemoglobin resistance to acid elution. Alternative methods to quantify FMH include the enzyme-linked antiglobulin test and flow cytometry. Only 1% of deliveries have a greater than 30 cc FMH—in such cases, RhIg doses are increased accordingly to protect against Rh(D) sensitization.