MCA Calculator

The core mathematical principle behind the MCA calculation involves scaling a patient's measured peak systolic velocity against the expected median velocity for a specific gestational age. The equation divides the measured velocity by the normal median velocity for that precise gestational week, expressed as: MoM = Measured Value / Median Value for Gestational Age. For twin pregnancies, independent calculations are performed for both the first and second twin to account for individual hemodynamic profiles.

Imagine a clinical scenario involving a singleton pregnancy at 28 weeks of gestation. The targeted ultrasound measures the Middle Cerebral Artery Peak Systolic Velocity (resultSingle) at 56 cm/s. Referring to standard obstetrical nomograms, the expected median velocity (medianSingle) for this gestational age is 40 cm/s. Applying the formula: MoM = 56 / 40. The resulting MoM is 1.40. This value indicates that the velocity is 40% above the median, which alerts the clinician to potential moderate-to-severe fetal anemia requiring further diagnostic evaluation.

Ensure that ultrasound equipment is properly calibrated and that angle of insonation is kept as close to zero degrees as possible to avoid velocity underestimation. Always verify that the gestational age is entered precisely in completed weeks and days, as median MCA-PSV values shift rapidly during the third trimester. Use this calculator as a supportive clinical aid alongside comprehensive biophysical profiles and clinical history.