MCA Calculator
Calculate middle cerebral artery peak systolic velocity median and MoM to assess fetal anemia risk during pregnancy.
Middle Cerebral Artery Doppler in Pregnancy
The middle cerebral artery (MCA) peak systolic velocity (PSV) measured by Doppler ultrasound is used to screen for fetal anemia, especially in Rh alloimmunization, parvovirus B19 infection, and other conditions causing hemolysis. This calculator computes the gestational-age-specific median and multiples of the median (MoM) using the Mari 2000 reference.
How MCA MoM Is Calculated
Mari et al. (2000) established a linear model on the natural log scale: ln(MCA-PSV) = 2.31 + 0.046 × gestational age in weeks. The median PSV equals e(2.31 + 0.046 × GA). MoM is the measured PSV divided by the median for the selected gestational age.
Interpretation Thresholds
MoM below 1.5 is generally considered normal. MoM ≥ 1.5 suggests moderate fetal anemia risk and warrants further evaluation. MoM ≥ 1.55 indicates severe anemia risk and requires urgent specialist assessment. Clinical decisions should incorporate full Doppler assessment, maternal history, and laboratory findings.
Frequently Asked Questions
What gestational ages are supported?
This calculator supports gestational ages from 14 to 40 weeks, matching the range used in the Mari 2000 reference equation.
What MCA-PSV value should I enter?
Enter the peak systolic velocity in cm/s from your MCA Doppler ultrasound report, measured as close to the internal carotid artery origin as possible with the beam aligned to blood flow.
What does a MoM of 1.5 or higher mean?
A MoM ≥ 1.5 suggests increased risk of moderate fetal anemia. Values ≥ 1.55 suggest severe anemia. Referral to maternal-fetal medicine and possible cordocentesis or intrauterine transfusion may be indicated based on full clinical context.
Can this calculator diagnose fetal anemia?
No. MoM is a screening aid. Definitive diagnosis requires specialist interpretation, serial Doppler measurements, and often invasive testing such as cord blood sampling.
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