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 redistribution of cardiac output to the brain due to the fetal head sparing theory.

See also

Ultrasound - obstetric
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Article information

rID: 33737
Section: Approach
Synonyms or Alternate Spellings:
  • Fetal MCA PI
  • Fetal MCA pulsatility index (PI)
  • Fetal middle cerebral artery (MCA) pulsality index (PI)

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Cases and figures

  • Case 1: 3rd trimester normal MCA Doppler
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