Prediction of severe fetal anemia in red blood cell alloimmunization after previous intrauterine transfusions.

OBJECTIVE: This study was undertaken to determine the detection of fetal anemia and false-positive rates by fetal middle cerebral artery peak systolic velocity (MCA-PSV) and the estimated daily decrease of hemoglobin (Hb) in red blood cell alloimmunized pregnancies that had previous fetal transfusions.

STUDY DESIGN: We examined the relation between MCA-PSV measured before cordocentesis, and fetal Hb at the time of the second (n = 42) and third (n = 31) intrauterine blood transfusions. In addition, the daily Hb drop between the transfusions was calculated.

RESULTS: The MCA-PSV provided significant prediction of severe anemia (Hb deficit > or = 6 g/dL) for the second but not for the third transfusion. Detection of 95% of severely anemic fetuses was achieved with a false-positive rate of 37% for the second transfusion and 90% for the third, compared with 14% in our previous study for the first transfusion. In patients who had received 2 previous transfusions, the only significant predictor of fetal anemia was the estimation of the Hb from the measured posttransfusion Hb after the second transfusion and the assumption that the rate of decrease in fetal Hb is 0.3 g/dL per day.

CONCLUSION: Prediction of severe fetal anemia after one transfusion is less accurate than in nontransfused fetuses. The MCA-PSV is not useful in predicting severe anemia in fetuses that already had 2 previous transfusions.