MCA-PSV for suspected fetal anemia
Use this calculator to estimate the expected median MCA peak systolic velocity for gestational age and to compute multiples of the median (MoM). MCA-PSV is widely used as a noninvasive screening test for moderate or severe fetal anemia, commonly using 1.5 MoM as the action threshold
MCA Peak Systolic Velocity Calculator
Enter gestational age and the observed MCA peak systolic velocity (PSV) to compute the expected median PSV, MoM, and plot the result on the graph.
Interpretation
Median MCA-PSV is shown for the selected gestational age. Enter an observed velocity to calculate MoM and display the point on the graph.
MCA-PSV by gestational age
Visualize the expected median curve, the 1.5 MoM threshold, and the observed value.
Blue line = expected median MCA-PSV. Dashed amber line = 1.5 MoM threshold. Enter an observed MCA-PSV to plot the red point.
Technique
- Fetus should be at rest without breathing or body movements.
- Obtain an axial view of the fetal head and identify the Circle of Willis with color Doppler (Image A).
- Enlarge the MCA so it occupies at least 50% of the screen; use a 1 mm sample volume placed about 2 mm from the MCA origin from the internal carotid artery (Image B).
- Align the ultrasound beam as close to parallel to flow as possible (ideal angle ≈ 0°).
- Record the highest reproducible PSV and repeat measurement at least 3 times.
- If the result is unexpected or near a management threshold, verify technique and consider repeat or confirmatory Doppler assessment when clinically appropriate.