Cerebroplacental ratio
Cerebroplacental ratio (CPR) is an obstetric ultrasound tool used as a predictor of adverse pregnancy outcome in both small for gestational age (SGA) and appropriate for gestational age (AGA) fetuses. An abnormal CPR reflects redistribution of cardiac output to the cerebral circulation, and has been associated with intrapartum fetal distress, increased rates of emergency Cesarean and NICU admissions and poorer neurological outcomes.
It is calculated by dividing the Doppler pulsatility index of the middle cerebral artery (MCA) by the umbilical artery (UA) pulsatility index:
CPR = MCA PI / UA PI
The index will reflect mild increase in placental resistance with mild reductions in the fetal brain vascular resistance. An abnormal cerebroplacental ratio may result in the following conditions:
- low normal range MCA and upper normal range UA PI
- abnormal low MCA and normal UA PI
- abnormal low MCA and high UA PI
It follow then that detection of perinatal risk based on CPR may occur in the setting of reassuring UA PI (but abnormal MCA), or even if both UA and MCA PI are within the normal range.
Various studies have variably defined the threshold of abnormal CPR as either ratio <1ref, ratio <1.08ref, in terms of MoMref or based on centiles. The only longitudinal study known to the article editor at the time of writing defines abnormal CPR as <5th centile2.
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Ultrasound - obstetric
- ultrasound (introduction)
- obstetric ultrasound
- first trimester and early pregnancy
- ectopic pregnancy
- multiple gestations
- subchorionic hematoma
- failed early pregnancy
-
second trimester
- fetal biometry
- fetal morphology assessment
- fetal echocardiography views
- nonvisualisation of the fetal stomach
-
soft markers
- nuchal fold thickness
- ventriculomegaly
- absent nasal bone
- choroid plexus cysts
- enlarged cisterna magna
- shortened fetal long bones
- echogenic intracardiac focus (EIF)
- echogenic fetal bowel
- aberrant right sublavian artery
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- single umbilical artery
- sandal gap toes
- amnioreduction
- Doppler ultrasound
- nuchal translucency
- 11-13 weeks antenatal scan
- chorionic villus sampling (CVS) and amniocentesis
- placenta
- other