Variables That Affect the Middle Cerebral Artery Peak Systolic Velocity in Fetuses with Anemia and Intrauterine Growth Restriction

Abstract

We have previously reported that the fetal middle cerebral artery (MCA) peak systolic velocity (PSV) increases in anemic fetuses and in fetuses with intrauterine growth restriction (IUGR). We hypothesized that the pathophysiology for the increased MCA PSV is different in anemic and IUGR fetuses. Thus the aim of this study was to determine the factor(s) among fetal umbilical vein blood pH, Po2, Pco2, and hemoglobin that might affect the MCA PSV in fetuses with anemia and IUGR. This study included two groups of fetuses. The first group included fetuses at risk for anemia because of red cell alloimmunization, whereas the second group included IUGR fetuses. For both groups of fetuses, we determined hemoglobin, umbilical vein blood gases -- at cordocentesis in anemic fetuses and immediately after cesarean delivery in IUGR fetuses -- and MCA PSV before cordocentesis, or before delivery. The relationship between MCA PSV and the hemoglobin, Po2, Pco2, and pH values for the anemic and the IUGR fetuses were assessed by regression analysis using multiples of the mean. There were 14 fetuses in the first group and 22 fetuses in the second group. In the first group, the only parameter that was related to MCA PSV was the fetal hemoglobin (R2 = 0.34; p < 0.05); in fetuses with IUGR, the Pco2 (R2 = 0.36; p < 0.01) and the PO2 (R2 = 0.30; p < 0.01) correlated well with the MCA PSV, whereas no relationship was found between the MCA PSV and the hemoglobin. The data indicate that the mechanism of high MCA PSV is different in anemic and nonanemic IUGR fetuses, and suggest that the process of cerebral autoregulation is present in the preterm IUGR fetus.