MCA Peak Systolic Velocity (MoM) — Twin Calculator

Enter gestational age and the observed MCA peak systolic velocity (PSV) for Twin A and Twin B to compute expected median PSV, MoM for each twin, and Δ MCA-PSV. MoM uses Klaritsch MCDA reference medians (15–37w) (linear interpolation by days).

weeks
Alerts: MoM ≥ 1.5  |  ΔMoM > 0.50
Expected Median MCA PSV
Reference used
Twin A — MoM
Twin B — MoM
Δ MCA PSV (|A − B|)
Δ MoM (|MoM A − MoM B|)

MoM = observed PSV / expected median PSV. Primary reference: Klaritsch MCDA medians (15–37w) with linear interpolation by days. Outside 15–37w, the calculator falls back to the Mari singleton formula used on the Perinatology MCA page. Common screening thresholds (context-dependent): MoM ≥ 1.5 (anemia risk) and ΔMoM > 0.50 (intertwin discordance/TAPS suspicion).

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 ≥ 50% of the screen; use 1 mm sample volume placed ~2 mm from MCA origin from the internal carotid artery (Image B).
  • Align the ultrasound beam parallel to flow (angle ≈ 0°) and record the highest PSV; repeat measurement at least 3 times.