Prediction of fetal anemia with Doppler measurement of the middle cerebral artery peak systolic velocity in pregnancies complicated by maternal blood group alloimmunization or parvovirus B19 infection.

OBJECTIVES: To confirm the relationship between the middle cerebral artery peak systolic velocity (MCA PSV) and hemoglobin values in fetuses at risk for anemia (due to maternal blood group alloimmunization or parvovirus B19 infection) and to investigate the clinical value of this method in the management of these pregnancies regardless of previous transfusions.

SUBJECTS AND METHODS: Forty singleton pregnancies, 30 affected by alloimmunization and 10 by intrauterine parvovirus B19 infection, were referred to our tertiary center between 1998 and 2000. All cases underwent Doppler measurement of the MCA PSV immediately before fetal blood sampling and just before and after intrauterine transfusion. Hemoglobin determination was always performed after diagnostic cordocentesis, before starting and after terminating fetal transfusion.

RESULTS: Overall, we performed 165 fetal blood samplings (hemoglobin values) and obtained 165 corresponding MCA PSV values, 140 in pregnancies complicated by red-cell alloimmunization and 25 by parvovirus B19 infection. In order to adjust for the effect of gestational age on the measurements, the data were expressed in multiples of the median (MoM). We found a good correlation between MCA PSV MoM and Hb MoM in both groups (alloimmunization, r2 = 0.6; y = 2.21 - 1.41 x + 0.24 x 2; parvovirus infection, r2 = 0.68; y = 2.09 - 0.58 x - 0.16 x 2). The reduction of post-transfusion MCA PSV values was statistically significant ( P < 0.0001). Using a threshold of 1.29 for MoM PSV, the sensitivity and the specificity of MCA pulsatility indices on pretransfusion values in predicting any degree of fetal anemia (Hb < or = 0.84 MoM) were 73.1% and 81.5% in the alloimmunization group and 100% and 100% in the parvovirus infection group, respectively.

CONCLUSION: We can confirm the presence of an inverse correlation between MCA PSV measurements and hemoglobin values in fetuses at risk for anemia due to maternal blood group alloimmunization and fetal parvovirus B19 infection. The MCA PSV is a reliable method for the prediction of anemia not only in fetuses before the first intrauterine transfusion, but also in those which have undergone one or more transfusions, with good sensitivity and specificity in both groups of fetuses at risk.