Prediction of fetal anemia in rhesus disease by measurement of fetal middle cerebral artery peak systolic velocity

Abstract

Objective In red blood cell (RBC) isoimmunized pregnancies fetal anemia is associated with a hyperdynamic circulation. The aim of the present study was to examine further the possible value of fetal middle cerebral artery peak systolic velocity (MCA-PSV) in the management of affected pregnancies. Methods A reference range of fetal MCA-PSV with gestation was constructed from the study of 813 normal singleton pregnancies at 20–40 weeks' gestation. Fetal MCA-PSV was also measured in 58 fetuses from RBC isoimmunized pregnancies, with maternal hemolytic antibody concentration of >15 IU/mL at 19–38 weeks' gestation and within 10 days of measurement of fetal hemoglobin concentration in blood obtained either by cordocentesis (n = 43) or at delivery (n = 15). In the RBC isoimmunized pregnancies each of the measured MCA-PSV and hemoglobin concentrations was expressed as a delta value (difference in SDs from the normal mean for gestation). Regression analysis was used to determine the significance of the association between delta MCA-PSV and delta fetal hemoglobin concentration. Results In the normal pregnancies there was a significant increase in fetal MCA-PSV with gestation (mean MCA-PSV = 10^{0.0223 × GA + 0.963}). In RBC isoimmunized pregnancies the fetal MCA-PSV was increased and there was a significant association between delta MCA-PSV and delta hemoglobin concentration (delta hemoglobin = (delta MCA-PSV + 0.093)/−0.356; R² = 0.638, P < 0.0001). An MCA-PSV of mean + 1.5 SDs detected 96% of severely anemic fetuses, with a hemoglobin deficit of at least 6 SDs, for a false-positive rate of 14%. Conclusion Measurement of fetal MCA-PSV is a useful method of assessing fetal anemia. In the clinical management of isoimmunized pregnancies a cut-off in MCA-PSV of mean + 1.5 SDs can identify nearly all severely anemic fetuses with a low false-positive rate. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.