Abnormal Cerebroplacental Ratio as a Marker of Fetal Compromise

Physiologic Mechanism

The American College of Radiology suggests that an abnormal cerebroplacental ratio (CPR) indicates early fetal cerebral vasodilation, representing a sensitive marker of placental insufficiency and fetal compromise, with a brain-sparing effect preceding detectable placental resistance changes 1, 2
Decreased middle cerebral artery (MCA) pulsatility index reflects cerebral vasodilation in response to fetal hypoxemia, representing the brain-sparing effect, and can occur independently of umbilical artery resistance increases 3, 4
The fetus redistributes blood flow to protect vital organs, such as the brain, heart, and adrenals, even when placental function is only mildly impaired, as indicated by an abnormal CPR 3

An abnormal CPR may be an earlier predictor of adverse outcome than umbilical artery Doppler abnormalities alone, detecting fetal adaptation before umbilical artery changes become apparent 1, 2, 5
Studies demonstrate that CPR abnormalities precede biophysical profile changes and umbilical artery Doppler abnormalities in the progression of fetal compromise, according to the American College of Radiology 2

The American College of Obstetricians and Gynecologists recommends repeat umbilical artery Doppler every 1-2 weeks initially to monitor for progression when CPR is abnormal but umbilical artery Doppler remains normal 6
Weekly cardiotocography (CTG) should be included as part of fetal surveillance when CPR is abnormal 7
Fetal growth should be assessed every 2-3 weeks, and amniotic fluid volume should be monitored as a marker of chronic placental insufficiency when CPR is abnormal 2, 5, 6

Current guidelines state that there is insufficient evidence to use CPR as a stand-alone test for clinical decision-making, and it should be incorporated as a component of comprehensive fetal surveillance, according to the American College of Radiology 1, 2, 3
The American College of Radiology recommends reporting pulsatility index to facilitate CPR calculation, and CPR assessment should be considered in all fetuses undergoing third-trimester ultrasound 1, 3