Prediction of fetal anemia by middle cerebral artery peak systolic velocity in pregnancies complicated by rhesus isoimmunization.

OBJECTIVES: To study the correlation of peak systolic velocity in the middle cerebral artery with hemoglobin concentration in fetuses at risk of anemia due to Rhesus isoimmunization. DESIGN: Peak systolic velocity of middle cerebral artery (MCA-PSV) was measured before 66 cordocentesis procedures in 20 isoimmunized fetuses. Reference values were derived from a study of 300 control fetuses. MCA-PSV values and hemoglobin concentrations were expressed as multiples of the median (MoM) for gestational age. The following hemoglobin concentration MoM thresholds defined degrees of anemia: mild, between 0.83 and 0.65; moderate, between 0.64 and 0.55; and severe, less than 0.55. Regression analysis was performed and receiver-operator-characteristic curves were constructed to determine the diagnostic accuracy of different thresholds of MCA-PSV for the prediction of moderate to severe anemia, either at the initial or repeat cordocentesis procedures. RESULTS: The mean (+/-SD) gestational age at cordocentesis was 28.5+/-4.6 weeks. Moderate to severe anemia was observed on 29 (44%) and hydrops on 27 (41%) occasions. MCA-PSV correlated weakly with hemoglobin concentrations. At threshold values 1.50 MoM, the sensitivity, specificity, and negative predictive value for moderate to severe anemia were 9.0, 100, and 48.0% at the initial cordocentesis procedures, and 44.0, 96.0, and 73.0% at repeat cordocentesis procedures, respectively. CONCLUSIONS: Although MCA-PSV is highly specific, negative values do not rule out fetal anemia. Further research is required before it can be recommended in clinical practice.