• Non-invasive screening for suspected fetal anemia (e.g., Rh/Kell alloimmunization)
• Monitoring pregnancies at high risk for parvovirus B19 infection
• Surveillance in cases of suspected twin-anemia polycythemia sequence (TAPS)

• Fetal anemia reduces blood viscosity.
• Anemia triggers a hyperdynamic circulatory state (increased cardiac output) to maintain tissue oxygenation.
• The combination of thin blood and high output dramatically increases the peak systolic velocity (PSV) in the easily accessible Middle Cerebral Artery (MCA).

• Angle of insonation MUST be exactly 0 degrees. Any angle correction artificially alters the velocity readout and invalidates the algorithm.
• Measurement must be taken in the proximal third of the MCA, near its origin from the internal carotid.
• Avoid applying pressure to the maternal abdomen (fetal head compression artificially elevates velocity).
• Fetal breathing or overt movement will alter velocity; measure during a period of fetal apnea/quiescence.

• Verify measurement meticulously (repeat sequentially).
• If persistently ≥1.5 MoM and gestation < 35 weeks: Proceed to cordocentesis (Percutaneous Umbilical Blood Sampling - PUBS) for definitive hematocrit.
• Prepare cross-matched, irradiated, O-negative packed red blood cells for immediate intrauterine transfusion (IUT) during PUBS if anemia is confirmed.
• If ≥ 35 weeks: Consider expedited delivery rather than high-risk intrauterine transfusion.

Pioneered by Giancarlo Mari and the Collaborative Group for Doppler Assessment of the Blood Velocity in Anemic Fetuses. It revolutionized maternal-fetal medicine by nearly eliminating the routine use of invasive, risk-heavy serial amniocenteses (Liley curves for delta OD450).