Increase of fetal hematocrit decreases the middle cerebral artery peak systolic velocity in pregnancies complicated by rhesus alloimmunization.

Abstract

Our hypothesis for this study was that an increase in fetal hematocrit would decrease the middle cerebral artery peak systolic velocity. Seventeen pregnancies complicated by Rh alloimmunization were included in this study. Middle cerebral artery peak systolic velocity was studied by Doppler ultrasound before and after intrauterine transfusion with adult packed red blood cells (hematocrit = 80-85%). Mean gestational age at time of study was 27 weeks. Paired t-test was used for statistical comparison. A P value of < 0.05 was considered statistically significant. The fetal hematocrit ranged from 5.9% to 30% prior to the procedure, and it was 24.8-53.4%, following the procedure. Mean middle cerebral artery peak systolic velocity was 46.2 +/- 10.7 cm/s prior to the procedure, and it decreased to 31.7 +/- 9.5 cm/s following the procedure (P < 0.01). The increase of fetal hematocrit significantly decreases the middle cerebral artery peak systolic velocity supporting data that this Doppler measurement may be useful for the diagnosis of fetal anemia.