Peak systolic velocity of fetal middle cerebral artery to predict anemia in Red Cell Alloimmunization in un-transfused and transfused fetuses.

Objective: To assess the accuracy of middle cerebral artery peak systolic velocity (MCA-PSV) in prediction of severe fetal anemia resulting from Red Cell Alloimmunization (Anti-D) in un-transfused and transfused fetuses. In addition to comparing the accuracy of MCA-PSV and the estimation of the daily decline of fetal hemoglobin (Hb), to determine the appropriate time of subsequent transfusions.

Study Design: This was a retrospective study of a series of 84 anaemic fetuses due to Red Cell alloimmunization. During each in-utero transfusion session, measurements of (1)MCA-PSV, (2)pre- and (3)post-transfusion Hb levels were recorded. Receiveroperating characteristics (ROC) curves, negative and positive predictive values of MCA-PSV in predicting severe fetal anemia were calculated. Regression analysis assesses the correlation between fetal HB and MCA-PSV, and between observed and expected fetal hemoglobin levels.

Results: Eighty four anemic fetuses were included in the study and had an in-utero transfusion. The positive predictive value (PPV) of MCAPSV decreased sharply from 86.0 % at the first IUT, to 52.0 % and 52.1 % at the second and third IUTs respectively. According to the ROC curves, setting the cut-off at 1.70 MoM would provide the best performance of MCA-PSV with respect to the timing of the second and third IUT. Setting a higher threshold of 1.70 MoM for the 2nd and 3rd transfusions would increase the PPV from 52.0 % to 96.4 % at the second IUT, and from 52.1%-99.8 % at the third IUT.

Conclusion: In this study we suggest that a higher MCA-PSV (MoM 1.7 in compared to 1.5MOM) can accurately predict the recurrence of severe fetal anemia requiring serial IUTs. In transfused fetuses, MCAPSV accuracy to detect severe anemia decline slightly with increase number of IUT. In addition to that, the mean projected daily decrease in fetal hemoglobin has a similar accuracy to MCA-PSV in predicting moderate to severe fetal anemia.