MCA PSV Calculator — Middle Cerebral Artery Doppler (Fetal Anemia)
The MCA PSV calculator determines whether a measured middle cerebral artery peak systolic velocity is within normal range for gestational age, expressed as a Multiple of Median (MoM). A MoM ≥ 1.50 indicates likely moderate-to-severe fetal anemia.
tednov
cm/s
Likely moderate-to-severe fetal anemia
- 1
GA^0.871
28^0.871 = 18,2169Mari 2000 exponent — accounts for the non-linear rise in MCA-PSV with gestational age. - 2
Expected median MCA-PSV = 1.50 × GA^0.871
1.50 × 18,2169 = 27,33 - 3
MoM = measured PSV ÷ expected median
55 ÷ 27,33 = 2,01
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The MCA-PSV Multiple of Median is computed as: MoM = Measured PSV ÷ (1.50 × GA^0.871). A MoM ≥ 1.50 suggests moderate-to-severe fetal anemia and typically prompts invasive testing or fetal transfusion. Values above the 95th percentile (1.29 MoM) warrant close surveillance. Always interpret with specialist guidance.
Formula
How this is calculated
Middle cerebral artery (MCA) Doppler velocimetry is used in obstetrics to screen for fetal anemia non-invasively. When a fetus becomes anemic, cardiac output increases and blood viscosity decreases, causing MCA blood velocity to rise. The peak systolic velocity (PSV) in the MCA is compared to a gestational-age-specific reference value derived from the landmark Mari et al. (2000) study.
The expected median MCA-PSV for a given gestational age (GA, in weeks) is calculated using the formula: Median PSV = 1.50 × GA^0.871 cm/s. The measured value is then expressed as a Multiple of Median (MoM): MoM = measured PSV ÷ expected median. The clinical threshold is MoM ≥ 1.50, which in the Mari study had a sensitivity greater than 80% and specificity around 88% for detecting moderate-to-severe fetal anemia — without the need for invasive amniocentesis.
The 1.29 MoM level (the 95th percentile) is used as a secondary alert threshold. Gestational age should be measured by the same ultrasound unit used for the Doppler. Technique matters critically: angle of insonation should be <30°, and the measurement should be taken near the origin of the MCA from the circle of Willis with the fetus at rest. This calculator is for educational reference only; clinical decisions require interpretation by a qualified maternal-fetal medicine specialist.
Pogosta vprašanja
A MCA-PSV MoM ≥ 1.50 is the widely accepted threshold for moderate-to-severe fetal anemia (Mari et al., NEJM 2000). Values between 1.29 and 1.49 MoM exceed the 95th percentile and warrant close monitoring, while values below 1.29 MoM are generally considered within the normal range for gestational age.
MCA-PSV naturally increases throughout pregnancy as the fetal brain grows and cardiac output increases. The Mari formula (Median = 1.50 × GA^0.871) accounts for this progression, so a PSV of 55 cm/s is normal at 28 weeks but elevated at 20 weeks. Expressing the result as a MoM removes the gestational-age dependency.
Fetal anemia from red-cell alloimmunization (Rh disease, Kell, Duffy), parvovirus B19 infection, fetomaternal hemorrhage, twin-to-twin transfusion, and thalassemias are the primary causes. MCA-PSV is also used to monitor hydrops fetalis. Elevated values may also occur with fetal tachycardia or hypo-oxygenation.
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TG we-Calculate Editorial Team. (2026). MCA PSV Calculator — Middle Cerebral Artery Doppler (Fetal Anemia) [Online calculator]. TG we-Calculate. https://we-calculate.com/sl/calculator/mca-calculator
TG we-Calculate Editorial Team. "MCA PSV Calculator — Middle Cerebral Artery Doppler (Fetal Anemia)." TG we-Calculate. 2026. https://we-calculate.com/sl/calculator/mca-calculator.
TG we-Calculate Editorial Team, "MCA PSV Calculator — Middle Cerebral Artery Doppler (Fetal Anemia)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/sl/calculator/mca-calculator
@misc{wecalculate_mca_calculator, title = {MCA PSV Calculator — Middle Cerebral Artery Doppler (Fetal Anemia)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/sl/calculator/mca-calculator}}, year = {2026}, note = {TG we-Calculate} }
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