middle cerebral artery peak systolic velocity (MCA-PSV) has been successfully used for identification of fetuses at risk for anemia requiring fetal blood sampling or intrauterine transfusion. Preliminary studies suggested that MCA-PSV could be as well a useful diagnostic tool to estimate the interval between transfusions. The present study describes the results of a prospective protocol for the management of fetuses with red cell alloimmunization after the first intrauterine transfusion, where the interval between transfusions was decide solely on the basis of MCA-PSV. A longitudinal prospective study including non-hydropic fetuses at 20–35 weeks' gestational age (GA) with a previous intrauterine transfusion due to red-cell alloimmunization. MCA-PSV was assessed every 5 to 7 days. Intrauterine blood transfusion was indicated when the values were greater than 1.5 MoM. The value of the test to predict moderate to severe anemia (Hb levels < 0.65 MoM for GA) was evaluated with 2 × 2 tables statistical analysis. During the study period 18 intrauterine transfusions were performed in 15 patients (range 0–3), with a median interval between transfusions of 20.3 days (range 7–28). At blood sampling, moderate to severe anemia was present in 14/18 (78%) and mild anemia (Hb 0.84–0.65 MoM for GA) in 4/18 (22%). None of the cases was found to have no anemia at blood sampling, and none developed hydrops during follow-up. MCA-PSV reliably predicts moderate/severe anemia in fetuses previously transfused in utero, allowing its use as a unique tool to establish the interval between transfusions. As compared to our previous protocol (15 days), MCA-PSV resulted in a 5-days gain in the interval between transfusions, avoiding unnecessary procedures.