Cerebroplacental Ratio (CPR) Calculation Using Doppler Indices
The cerebroplacental ratio (CPR) is calculated as the ratio of the fetal middle cerebral artery (MCA) Doppler measurement to the fetal umbilical artery (UA) Doppler measurement.
CPR uses the same type of Doppler index for both vessels (e.g., PI with PI, or S/D with S/D).
Formula Using Pulsatility Index (PI)
CPR (PI-based)
[
\text{CPR}=\frac{\text{MCA-PI}}{\text{UA-PI}}
]
Formula Using S/D Ratio
CPR (S/D-based)
[
\text{CPR}=\frac{\text{MCA (S/D)}}{\text{UA (S/D)}}
]
Practical Index-Consistency Rules
CPR should be computed using the same Doppler index in the numerator and denominator (PI with PI, S/D with S/D).
CPR should be derived from third-trimester Doppler measurements of MCA and UA obtained in the same fetal condition/assessment session.