Middle cerebral artery Doppler: the value of a non-invasive test of fetal anaemia in the management of alloimmunised pregnancies

Abstract

We set out to determine the usefulness of fetal middle cerebral artery peak systolic velocity (MCA-PSV) in predicting fetal anaemia in Rhesus alloimmunised pregnancies before first and subsequent in-utero transfusions. This was a retrospective analysis of fetal MCA-PSV values and haematocrits (Hct) performed in 30 alloimmunised fetuses before their first intrauterine blood transfusion, and before 35 repeat transfusions. A MCA-PSV of greater than 1.5 MoM for gestation would have identified seven of eight severely anaemic fetuses (Hct < 22%) and 3/7 moderately anaemic fetuses (Hct 22–26%). Five fetuses with haematocrits > 26% would have been identified falsely, of which one had a Hct > 35%. Following one intrauterine transfusion the use of this test cut-off was less predictive, detecting 3/4 fetuses with severe anaemia but none of the four fetuses with moderate anaemia. A higher cut-off (1.69 MoM) was as sensitive but more specific in the prediction of severe anaemia. A lower threshold of 1.32 MoM would have identified of 2/4 fetuses with moderate anaemia, but only when utilising a cut-off value of 0.98 MoM could all the severe and moderately anaemic fetuses have been identified.