P06.02: Use of the 95th centile MCA PSV for the prediction of fetal anemia

Abstract

Objective: To evaluate the positive predictive value of the middle cerebral artery (MCA) Doppler peak systolic velocity (PSV) measurement >95th centile for the detection of fetal anemia in pregnancies complicated by red cell alloimmunization. Methods: A retrospective analysis of 41 patients over a 3 year period. In 47 cases an intrauterine fetal transfusion was undertaken between 21 and 35 weeks gestation because of suspected fetal anemia. Deviation of MCA PSV and hemoglobin from the mean/median were expressed as either Z-scores (SDs) or multiples of the median (MoM), respectively. The sensitivity of the 95th centile (>2SD) of MCA PSV for mild (<0.85 MoM) and moderate/severe (<0.65 MoM) anemia were calculated. Results: The sensitivity of the 95th centile of MCA PSV for mild and moderate/severe anemia was 97% and 100%, respectively. There were only 3 false positive MCA PSV tests, two of which were related to the presence of a coincidental fetoplacental vascular tumor causing a hyperdynamic circulation. Conclusions: The 95th centile of the MCA PSV appears to have an equal sensitivity with a low false positive rate for the detection of fetal anemia compared to the 66th centile (1.5MoM), which is the currently recommended standard. Use of the 95th centile would reduce the number of invasive tests required in the management of red blood cell isoimmunised pregnancies.