MCA-PSV Calculator - Fetal Anemia Risk

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Completed weeks of gestational age. Mari published reference values from 18 to 40 weeks; entries below 18 weeks extrapolate the curve and should be interpreted with caution. False-positive MoM values also become more common after 35 weeks.
weeks
Extra days beyond the completed weeks (0-6). Adds fractional precision to the gestational age.
days
Peak systolic velocity in the fetal middle cerebral artery measured by pulsed-wave Doppler. Measure as close to the internal carotid artery origin as possible with the beam angle at or near 0 degrees.
cm/s
Twin pregnancies may have slightly different reference distributions. The same 1.5 MoM action threshold is generally applied, but close surveillance is especially important.
MoM (Multiple of Median)Moderately elevated - close surveillance
1.49

Observed MCA-PSV divided by the expected median for gestational age

Expected median PSV37cm/s
1.5 MoM threshold55.5cm/s
PSV above 1.5 MoM threshold0cm/s
1.49 MoM
Normal<1Mildly elevated1-1.29Moderately elevated1.29-1.5Action threshold1.5+

MoM 1.49: moderately elevated - increased surveillance is appropriate.

  • At 28 weeks, the expected median MCA-PSV is 37.0 cm/s. The 1.5 MoM action threshold is 55.5 cm/s.
  • Values in the 1.29-1.5 range are above normal but have not yet reached the standard action threshold.
  • Close interval follow-up is typically recommended, often within 1 week.

Next stepDiscuss findings with a maternal-fetal medicine specialist. The cause of alloimmunization or anemia risk should be reviewed and a repeat scan planned.

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