Fetal middle cerebral artery pulsatility index
The fetal middle cerebral artery (MCA) pulsatility index (PI) is a key parameter used in fetal middle cerebral arterial Doppler assessment. It is calculated by subtracting the end-diastolic velocity (EDV) from the peak systolic velocity (PSV) and then dividing by the time-averaged (mean) velocity (TAV):
- PI = (PSV - EDV) / TAV
Practical points
The fetal MCA PI normally has a high value. The mean value (normal reference range) slowly decreases through gestation from around 28 weeks onwards. A low PI reflects the redistribution of cardiac output to the brain due to the fetal head sparing theory.
See also
Related Radiopaedia articles
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
- non-visualization 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 subclavian artery
- fetal pyelectasis / fetal renal pelvic dilatation
- single umbilical artery
- sandal gap toes
- amnioreduction
- Doppler ultrasound
- nuchal translucency
- 11-13 weeks antenatal scan
- chorionic villus sampling (CVS) and amniocentesis
- placenta
- other
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