ObjectiveThe purpose of this study was to investigate the placental passage of erythropoietin in a placental perfusion model ex vivo.MethodsIn an open system 18 placentas were perfused on both the maternal and the fetal side. Erythropoietin and a reference substance were added to either the maternal or fetal perfusion medium. In the first series of experiments, radiolabeled erythropoietin was added to the perfusion medium in four different concentrations to help determine the transfer rate of erythropoietin. Based on the results of these experiments unlabeled erythropoietin was added to the perfusate in three different concentrations. Radiolabeled erythropoietin was used in addition to erythropoietin because measuring radioactivity in a gamma counter is less expensive than measuring by immunoassay.ResultsAccumulation of radioactivity in the venous portion of the fetal circuit was only 3.21% of the activity added to the maternal circuit. No evidence of transfer of erythropoietin to the contralateral compartment was noted, regardless of whether the test substance was added maternally or fetally. These results were independent of the concentration used. The reference compound antipyrine showed a mean transfer rate of 27.9%, which is in keeping with previous results.ConclusionThere is no transport of erythropoietin across fetal membranes. This finding is particularly remarkable in view of results published recently indicating the placenta as a site of erythropoietin production. The lack of its transport across the human placenta is most likely due to its high molecular weight.