Objective The purpose of this study was to determine the clinical out come of i soimmunized pregnancies managed primarily by middle cerebral artery peak systoli c velocity. Study design A retrospective chart review was conducted of isoimmuni zed pregnancies that underwent ultrasound examinations from January 1, 2001, thr ough May 1, 2003. Ultrasound reports, laboratory tests, and maternal and neonata l charts were reviewed. Results Women with a clinically significant red blood ce ll antibody and titer value were included. The study population consisted of 39 women (40 pregnancies, 42 fetuses). Patients with a middle cerebral artery peak systolic velocity of ≥1.5 MoM were offered amniocentesis. Seven pregnancies had an abnormal middle cerebral artery peak systolic velocity. Three of these infan ts had significant anemia. Six of the 7 pregnancies required an exchange transfu sion. None of the 33 pregnancies (35 neonates) with normal middle cerebral arter y peak systolic velocity measurements resulted in a neonate with significant ane mia or severe hyperbilirubinemia. Conclusion The clinical outcome of these pregn ancies supports the use of middle cerebral artery peak systolic velocity measure ments in the management of isoimmunized pregnancies. Objective The purpose of this study was to determine the clinical out of of I soimmunized pregnancies managed primarily by middle cerebral artery peak systoli c velocity. Study design A retrospective chart review was conducted of isoimmuni zed pregnancies that underwent ultrasound examinations from January 1, 2001, thr ough May 1, 2003. Ultrasound reports, laboratory tests, and maternal and neonata l charts were reviewed. Results Women with a clinically significant red blood ce ll antibody and titer value were included. The study population consisted of 39 women (40 pregnancies, Six pregnancies had an abnormal middle cerebral artery peak peak systolic velocity. Three of these infan ts had significant anemia. Six of the 7 pregnancies required an exchange None of the 33 pregnancies (35 neonates) with normal middle cerebral arter y peak systolic velocity measur ements resulted in a neonate with significant ane mia or severe hyperbilirubinemia. Conclusion The clinical outcome of these pregnancies supports the use of middle cerebral artery peak systolic velocity measure ments in the management of isoimmunized pregnancies.