Fetal Anemia (MCA PSV)

MCA Peak Systolic Velocity

Fetal Anemia Surveillance (Mari et al.)

PSV (cm/s)

Weeks (GA)

Clinical Note: MCA-PSV > 1.5 MoM is the evidence-based threshold for invasive testing (cordocentesis) or intrauterine transfusion in alloimmunized pregnancies.

Guidelines & Evidence

Verified

Last Review: 2026-07-17

When to Use

Primary Clinical Uses

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)

When NOT to Use

Predictive value drops precipitously after 35 weeks of gestation. Do NOT use MCA-PSV as the sole determinant for delivery timing in late preterm/term fetuses. False positive rates surge near term.

How it Works

Pathophysiologic Basis

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).

Standard Thresholds

< 1.5 MoM	Reassuring (Mild or no anemia)
≥ 1.5 MoM	High risk for Moderate-to-Severe Anemia
≥ 1.55 MoM	Often correlates strongly with hematocrit <30%

Last Comprehensive Review: 2026-07-17

In Recent Clinical News

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Fetal Anemia (MCA PSV)

MCA Peak Systolic Velocity

When to Use

Primary Clinical Uses

When NOT to Use

How it Works

Pathophysiologic Basis

Standard Thresholds

Clinical Pearls

Measurement Precision Rules

Next Steps

Management of Elevated PSV (≥ 1.5 MoM)

The Evidence

Landmark Trial

Noninvasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization.

Origins & History

Dr. Giancarlo Mari

In Recent Clinical News

Fetal Anemia (MCA PSV)

MCA Peak Systolic Velocity

When to Use

Primary Clinical Uses

When NOT to Use

How it Works

Pathophysiologic Basis

Standard Thresholds

Clinical Pearls

Measurement Precision Rules

Next Steps

Management of Elevated PSV (≥ 1.5 MoM)

The Evidence

Landmark Trial

Noninvasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization.

Origins & History

Dr. Giancarlo Mari

In Recent Clinical News