The pathophysiology of fetal hydrops is still unclear. One factor that is believed to contribute to hydrops is hypoalbuminemia. Our research question was whether hypoalbuminemia in immune hydrops is causative or a secondary effect.Between 1987 and 2005, fetal blood samples were taken at the first fetal blood transfusion in 224 Rh-D alloimmunized pregnancies. We measured hemoglobin concentration and albumin concentration and assessed the severity of hydrops.A decrease in albumin concentration occurred only below a hemoglobin deficit of >8 SDs in 27 fetuses. In 161 nonhydropic, 44 mildly hydropic, and 19 severely hydropic fetuses, albumin concentrations were >2 SDs below the mean for gestational age in 6%, 14%, and 63%, respectively.Our finding that most fetuses with immune hydrops have an albumin concentration within the normal range (71%) suggests that hypoalbuminemia is unlikely to cause the initial development of immune hydrops.