Fetal MCA Doppler Assessment
MCA peak systolic velocity (PSV) correlates with fetal anemia risk. Use gestational age-adjusted medians to interpret Doppler measurements.
How to Use This Calculator
Perform standardized MCA Doppler
Use a transverse fetal head view with MCA near the circle of Willis, angle correction <15°, and sample close to the origin.
Enter exact gestational age
Use obstetric dating to determine weeks and days (16+0 to 40+6 weeks are supported).
Review risk stratification
MoM ≥1.55 is highly predictive of moderate/severe anemia and indicates need for specialist intervention.
Formula
Median PSV derived from gestational age–specific reference data (Mari et al., 2000).
MoM = Measured PSV ÷ Median PSV
Risk thresholds: MoM ≥1.55 (high risk), 1.45–1.54 (borderline), 1.0–1.44 (upper normal), <1.0 (normal)
Full Description
Middle cerebral artery Doppler is a key non-invasive tool for detecting fetal anemia, especially in pregnancies with red cell alloimmunization, parvovirus infection, or fetomaternal hemorrhage. Elevated MCA PSV reflects decreased blood viscosity in anemic fetuses. Serial measurements guide timing of intrauterine transfusions (IUT). Proper technique and consistent gestational dating are essential for interpretation.
Frequently Asked Questions
When should I start MCA Dopplers?
Begin at 18–20 weeks for pregnancies at risk of alloimmunization or prior fetal anemia, earlier if clinically indicated.
How often should monitoring occur?
Typically every 1–2 weeks, increasing to weekly or more frequently if MoM approaches treatment thresholds.
Does fetal heart rate affect PSV?
Yes. Tachycardia can increase PSV. Ensure the fetus is calm and heart rate is documented during measurement.
What if measurements are inconsistent?
Repeat the Doppler with optimal technique or refer to a maternal-fetal medicine specialist for confirmation.