Peak Systolic Velocity in the Middle Cerebral Artery (MCA-PSV) for Diagnosis of Fetal Anemia: Threshold 1.5 MoM
Clinical Role of MCA-PSV
Assessment of peak systolic velocity in the middle cerebral artery (MCA-PSV) is one of the most important targeted applications of Doppler ultrasound in complicated pregnancy for detection of suspected fetal anemia. According to current SMFM recommendations, MCA-PSV is the primary non-invasive method for detecting fetal anemia, replacing the previous reliance on determination of bilirubin in amniotic fluid for routine surveillance.
Threshold of 1.5 MoM
The value is expressed in multiples of the median (MoM). Elevation of MCA-PSV reflects hyperdynamic circulation characteristic of fetal anemia.
MCA-PSV in Twin Anemia-Polycythemia Sequence (TAPS)
Doppler assessment of MCA-PSV is not included in the Quintero classification for twin-to-twin transfusion syndrome (TTTS); however, it is widely used for diagnosis of twin anemia-polycythemia sequence (TAPS) in monochorionic pregnancy.
| Feature | Criterion |
|---|---|
| Donor MCA-PSV | > 1.5 MoM |
| Recipient MCA-PSV | < 1.0 MoM |
| Intertwин difference in MCA-PSV | > 0.5 MoM (large) |
TAPS is suspected when donor MCA-PSV > 1.5 MoM and recipient MCA-PSV < 1.0 MoM or when a significant (> 0.5 MoM) intertwin difference in MCA-PSV is present.
Technique and Variability
The validity of the method depends on correct measurement technique; factors affecting MCA-PSV have been described, including the combination of anemia and intrauterine growth restriction [to be clarified]. Systematic reviews and meta-analyses of the effectiveness of MCA-PSV for predicting anemia in both non-transfused and transfused fetuses have been published.
Frequently asked questions
What MCA-PSV threshold indicates fetal anemia?
The threshold value is >1.5 MoM. In the context of TAPS, this criterion is applied to donor MCA-PSV.
Does MCA-PSV replace amniotic fluid bilirubin testing?
Yes. According to SMFM recommendations, MCA-PSV is the primary non-invasive method for detecting fetal anemia, replacing the previous reliance on determination of bilirubin in amniotic fluid for routine surveillance.
How is TAPS diagnosed using MCA-PSV?
TAPS is suspected when donor MCA-PSV >1.5 MoM and recipient MCA-PSV <1.0 MoM, or when an intertwin difference in MCA-PSV >0.5 MoM is present.
Is MCA-PSV included in the Quintero classification for TTTS?
No, MCA-PSV is not a criterion in the Quintero classification for TTTS, but it is frequently used for assessment of TAPS.