Normal MCA Peak Systolic Velocity Values at 28 Weeks Gestation
At 28 weeks gestation, the normal middle cerebral artery peak systolic velocity (MCA-PSV) is 36.9 cm/s (1.0 MoM), with values up to 46.6 cm/s (1.29 MoM) considered normal, and values ≥55.4 cm/s (1.50 MoM) indicating potential fetal anemia requiring further evaluation. 1
Reference Values for 28 Weeks
Based on the Society for Maternal-Fetal Medicine (SMFM) Clinical Guideline, the standardized MCA-PSV values at 28 weeks are:
- 1.0 MoM (median): 36.9 cm/s
- 1.29 MoM: 46.6 cm/s
- 1.50 MoM (threshold for anemia): 55.4 cm/s
- 1.55 MoM: 57.2 cm/s
Clinical Interpretation
Normal Range
Values below 1.29 MoM (46.6 cm/s at 28 weeks) are considered normal and require no additional intervention beyond routine prenatal care.
Surveillance Zone
Values between 1.29-1.49 MoM warrant closer monitoring with repeat measurements, particularly if there are risk factors for fetal anemia (red cell alloimmunization, parvovirus exposure, twin-twin transfusion syndrome, or fetomaternal hemorrhage). 1
Action Threshold
Values ≥1.50 MoM (≥55.4 cm/s at 28 weeks) indicate moderate to severe fetal anemia with nearly 100% sensitivity and should prompt consideration for fetal blood sampling and potential intrauterine transfusion. 1 The false-positive rate at this threshold is approximately 12%, which is acceptable given the high sensitivity for detecting clinically significant anemia. 1
Important Technical Considerations
Proper Measurement Technique
To ensure accurate values, the MCA-PSV must be measured correctly:
- Obtain measurements during fetal rest (no breathing or movements)
- Sample the MCA close to its origin from the internal carotid artery
- Maintain the ultrasound beam angle as close to 0 degrees as possible
- Repeat measurements at least 3 times and use the highest value
- The MCA should occupy >50% of the image when zoomed
Common Pitfalls to Avoid
Critical caveat: Elevated MCA-PSV >1.5 MoM with normal hemoglobin occurs in approximately 6% of cases and may be associated with intracranial hemorrhage, maternal/fetal acidosis, hypoxic-ischemic encephalopathy, or idiopathic nonimmune hydrops rather than anemia. 2 Therefore, while MCA-PSV is highly sensitive for anemia, other pathology should be considered when fetal blood sampling reveals normal hemoglobin despite elevated velocities.
Fetal movement or breathing can artificially alter heart rate and affect MCA-PSV measurements, leading to false results. Always ensure the fetus is in a quiescent state during measurement. 1
Monitoring Frequency
For pregnancies at risk for fetal anemia (critical antibody titers reached), weekly MCA-PSV measurements should be performed starting at 16 weeks gestation and continuing through 35 weeks. 3 More frequent monitoring may be indicated with higher MoM values or other concerning ultrasound findings. 1