Objective: To determine placental pathology and immune response at the maternal-fetal interface in pregnancies conceived by IVF via egg donation compared with nondonor IVF pregnancies. Design:... Show moreObjective: To determine placental pathology and immune response at the maternal-fetal interface in pregnancies conceived by IVF via egg donation compared with nondonor IVF pregnancies. Design: Retrospective case-control study. Setting: Academic medical center. Patient(S): The study population included 20 egg donor and 33 nondonor IVF pregnancies of >24 weeks' gestation. Intervention(s): None. Main Outcome Measure(s): Perinatal complications (gestational hypertension, abruption, preterm delivery, cesarean section), microscopic features indicating ail immune response and trophoblast damage, and characterization of inflammatory cells using immunohistochemistry. Result(S): There was ail increase in gestational hypertension and preterm delivery in egg donor pregnancies. Dense fibrinoid deposition in the basal plate with severe chronic deciduitis containing significantly increased numbers of T helper and natural killer cells were demonstrated in egg donor placentas. Trophoblast damage was also increased in the preterm egg donor group. Conclusion(S): There are significant histological and immunohistochemical differences between the placentas of egg donor and nondonor IVF pregnancies. The increased immune activity and fibrinoid deposition at the maternal-fetal interface of egg donor pregnancies Could represent a host versus graft rejection-like phenomenon. (Fertil Steril (R) 2010;93:397-404. (C)2010 by American Society for Reproductive Medicine.) Show less