The effect of intrauterine transfusion on middle cerebral artery Doppler velocimetry (MCA Vp) on anaemic fetuses

Abstract

Fetal middle cerebral artery peak systolic velocity (MCA Vp) has been used as a screening test for fetal anaemia. The pathophysiology of MCA autoregulation during and post-intrauterine transfusion (IUT) remains unknown. A prospective study investigated the effects of IUT on the MCA Vp on anaemic fetuses and correlated this to alterations in haematological rheology and plasma volume expansion. During 11 IUTs (GA: 19–28 weeks) MCA Vp insonation before, immediately after, 10 minutes, 20 minutes, 30 minutes and 120 minutes post-IUT were measured and corrected for fetal heart rate. The pre- and post-transfusion haemoglobin, haematocrit, volume and rate of transfusion were recorded. All data are means and ranges. Data were compared pre- and post-transfusion by Wilcoxon's rank sum test and regression analysis. The MCA Vp prior to IUT was elevated for GA in all cases (61.5 cm/s: range 45.0–90.3 cm/s). There was a significant decrease in MCA Vp post-IUT (36.7 cm/s: range 36.7–61.3 cm/s; P < 0.05). The fall in MCA Vp persisted at 120 minutes. The mean fetal haematocrit prior to IUT was 23.5% (range 5.1–35.0%), increasing to 41.7% post-transfusion. The MCA Vp was inversely correlated with fetal haematocrit (P = 0.03). There was no correlation between the change of MCA Vp and rate of change of haematocrit or plasma volume expansion.