Purpose: To determine the role of fetal multiples of the median of middle cerebral artery peak systolic velocity (MoM MCA-PSV), in predicting the degree of fetal anemia for determination of the best timing for the second intrauterine intravascular transfusion (IUIVT) in hydropic fetuses with Rh alloimmunization. Materials and Methods: Prospective study of 30 monofetal pregnancies with maternal Rh D alloimmunization and hydrops fetalis, from 2005 to 2012 that underwent first and second IUIVT were assessed. Results: Thirty IUIVT were performed at 26.9 weeks (standard deviation, SD 4.3). Mean interval to the second procedure was 11.23 (SD 6.21) days and average hematocrit decline rate was 1.45%/day. The study did not demonstrated statistical significance between MCA-MoM-3 before the second IUIVT, and the mean decline rate in fetal hematocrit levels (expressed in percentage/day) r = 0.220; p = 0.242, and between MCA-MoM-3 and the time interval between both procedures (T) r = -0.157; p = 0.408. Conclusion: The measurements fetal MoMMCA before every IUIVT cannot be useful as predictor for the best timing for the next IUIVT, but it can be useful in predicting severity of fetal anemia.