RESUMO
OBJECTIVE: To assess the peak systolic velocity in the middle cerebral artery (PSV-MCA) in the prediction of fetal anemia in case of severe red-cell alloimmunization. METHODS: A prospective study, from January 2003 to April 2006, of 47 consecutive pregnancies with severe alloimmunization. Fetal surveillance was based on titration and dosage of antibodies, ultrasound scans, and doppler for PSV-MCA measurement up to twice a week. A fetal blood sampling and in utero transfusion was performed in case of increase in PSV-MCA above 1.5 multiples of the median (MoM), and/or signs of hydrops on ultrasound. Severe fetal anemia was defined by fetal hemoglobin below 0.55MoM for gestational age. Analyses performed included the correlation between PSV-MCA and fetal hemoglobin, the value of PSV-MCA in the prediction of severe fetal anemia, and the determination of adequate threshold for intervention based on ROC curve analysis. RESULTS: Four hundred and eighty-five PSV-MCA were performed in 47 high-risk pregnancies, of which 125 were coupled with hemoglobin measurement by fetal blood sampling. There is a significant negative correlation between PSV-MCA and fetal hemoglobin (R2=0.6545 ; p<0.0001). Based on all prospective data, the negative predictive value of PSV-MCA was 97.8 %, sensitivity was 86.7 %, with a false positive rate of 12.2%. Area under the ROC curve was 0.85 (IC 95 %, 0.742-0.927 ; p<0.0001), suggesting an excellent value of this test. When switching the threshold for intervention from 1.5 to 1.6MoM, the positive predictive value increased, without decrease in sensitivity or negative predictive value. CONCLUSION: This study confirms the correlation between PSV-MCA and fetal hemoglobin. It allows a decrease of invasive procedures in the follow-up of pregnancies with severe red-cell alloimmunization.