Middle Cerebral Artery Pulsatility Index (unitless) Enter the MCA PI value from your Doppler ultrasound (e.g., 1.80)

Umbilical Artery Pulsatility Index (unitless) Enter the UA PI value from your Doppler ultrasound (e.g., 0.90)

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Normal Doppler Values Reduced CPR Scenario

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This calculator is a screening tool only, not a diagnostic instrument. It is not intended to replace professional medical evaluation. Consult a healthcare provider.

What Is Cerebroplacental Ratio

Cerebroplacental ratio, or CPR, is a number that compares blood flow in two parts of a baby's body during pregnancy. It looks at the middle cerebral artery in the brain and the umbilical artery that connects to the placenta. When the baby is not getting enough oxygen or nutrients, the body may send more blood to the brain. The CPR number helps show if this shift in blood flow may be happening.

How Cerebroplacental Ratio Is Calculated

Formula

To find the cerebroplacental ratio, the middle cerebral artery pulsatility index is divided by the umbilical artery pulsatility index. The pulsatility index measures how much blood flow changes between heartbeats in each artery. A higher MCA PI means more resistance in the brain artery, and a higher UA PI means more resistance in the umbilical artery. When the brain artery resistance drops and the umbilical artery resistance stays the same or rises, the CPR goes down. A lower CPR may suggest the baby's body is sending more blood to the brain.

Why Cerebroplacental Ratio Matters

Knowing the cerebroplacental ratio may help doctors watch for changes in how a baby is growing during pregnancy. A ratio that falls below common reference points could be an early sign that the baby may need closer monitoring or further testing to check on growth and well-being.

Why Blood Flow Redistribution Is Important for Fetal Monitoring

When a baby in the womb is not getting enough oxygen or nutrients, the body may change how blood flows to protect the brain. This is called the brain-sparing effect. If this change is missed, it may mean that a growth problem or other concern goes unnoticed for longer. Checking the CPR may help catch this shift early so that the care team can decide if more tests or follow-up visits may be helpful.

For Different Stages of Pregnancy

The meaning of a CPR value may change based on how far along the pregnancy is. Early in pregnancy, normal CPR values tend to be lower. As the pregnancy goes on, the normal range shifts. A CPR value that is normal at one stage may be different at another. Doctors often use gestational age-specific charts to help read the number more accurately.

Cerebroplacental Ratio vs Individual Pulsatility Index

CPR is different from looking at just the MCA PI or UA PI on its own. Each pulsatility index tells you about one artery. CPR puts both numbers together to show the bigger picture of how blood is being shared. Looking at only one index may miss the shift in blood flow that CPR is designed to catch.