Fetal middle cerebral arterial Doppler assessment

Fetal middle cerebral arterial (MCA) Doppler assessment is an important part of assessing fetal cardiovascular distressfetal anaemia or fetal hypoxia. In the appropriate situation it is a very useful adjunct to umbilical artery Doppler assessment. It is also used in the additional work up of 

Radiographic assessment

Doppler ultrasound

For an accurate measurement, the fetal head should be in the transverse plane. An axial section of the brain, including the thalami and the sphenoid bone wings, should be obtained and magnified. The MCA vessels are often found with colour or power Doppler ultrasound overlying the anterior wing of the sphenoid bone near the base of the skull. The reading should be obtained close to its origin in the internal carotid artery as the systolic velocity decreases with distance from the point of origin of this vessel. An angle of insonation of < 15o should be used; typically, an angle that approximates zero degrees can be achieved by moving the transducer on the maternal abdomen. 

Parameters used include

Interpretation
  • in the normal situation the fetal MCA has a high resistance flow which means there is minimal antegrade flow in fetal diastole
  • in pathological states this can turn into a low resistance flow mainly as a result of the fetal head sparing theory
  • paradoxically in some situations such as with severe cerebral oedema, the flow can revert back to a high resistance pattern when the pathology has not yet resolved - this is a very poor prognostic sign
  • cerebroplacental ratio: > 1:1 is normal and <1:1 is abnormal 

See also


Ultrasound - obstetric

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