Prediction of Fetal Anemia in Subsequent Transfusions: Is There a Need to Change the Threshold of the Peak Systolic Velocity of the Middle Cerebral Artery?

Background: Peak systolic velocity (PSV) of the middle cerebral artery (MCA) shows 100% sensitivity for predicting fetal anemia before the first intrauterine transfusion (IUT). However, its ability to predict subsequent transfusions has remained mostly controversial.

Objective: To assess if there is a need to change the threshold of MCA-PSV from 1.5 to 1.69 multiples of the median (MoM) to predict fetal anemia and the need for subsequent IUT.

Methods: This is a retrospective audit, wherein case records of mothers who underwent IUT at the Bangalore Fetal Medicine Centre between April 2008 and May 2017 were reviewed; 86 cases were included, and the data were analyzed using MS Excel. The MCA-PSV and pretransfusion Hb were converted into MoM. 40 fetuses that had more than 1 IUT were included in the analysis. -

Results: 31/40 fetuses that had >1 IUT had an MCA-PSV >1.5 MoM, of which 29 were anemic according to the post-IUT Hb MoM. 20/29 (69%) had an MCA-PSV >1.69, whereas 9/29 (31%) had an MCA-PSV between 1.5 and 1.69 MoM. Our study shows that changing the MCA-PSV threshold from 1.5 to 1.69 MoM will reduce the detection of fetal anemia and hence the need for repeat IUT by 31%.

Conclusions: Increasing the fetal MCA-PSV threshold from 1.5 to 1.69 will miss out one-third of the fetuses that will require a 2nd, 3rd, or 4th IUT. This is more relevant in geographical areas where the parents must travel long distances for IUTs, which are performed in tertiary fetal care centers.