MCA Calculator for Fetal Anemia

Screens for risk of fetal anemia based on middle cerebral artery measurement during doppler scan in pregnancy.

Refer to the text below the tool for more information about the MCA velocity by gestational age in weeks and the multiple of median (MoM value).


The middle cerebral artery is one of the three largest vessels that supply the brain with blood and is very visible on Doppler ultrasound during fetal wellbeing checks.


  • Middle Cerebral Artery Peak Systolic Velocity (MCA-PSV) = e (2.31 + 0.046 GA)
  • Multiple of the Median (MoM) = Doppler MCA peak systolic velocity / MoM 1 (Median)

With the following properties: R2=0.78, P<0.001.

The risk of fetal anemia is highest at observed peak systolic velocities of 1.5 times the median or higher.


Gestational age (weeks)
Doppler MCA peak systolic velocity
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Multiple of Median and MCA Velocity

The middle cerebral artery is one of the three largest vessels that supply the brain with blood and is very visible on Doppler ultrasound during fetal wellbeing checks. This can replace serial amniocenteses for fetal anemia screening.

Evaluation of the MCA is employed in:

  • Diagnosis of growth restriction;
  • Screening and assessment risk of pre-eclampsia;
  • Suspected serological Rh+/Rh- conflict;
  • Complications in multiple pregnancy.

There are established values of the median peak systolic velocity, based on gestational age (week 18 to 40) that can be retrieved from published tables or estimated through:

  • Middle Cerebral Artery Peak Systolic Velocity (MCA-PSV) = e (2.31 + 0.046 GA)
  • With the following properties: R2=0.78, P<0.001.

The median MCA-PSV is then compared with the observed MCA during Doppler ultrasound, to determine the Multiple of the Mean (MoM) which s a measure of how the observed MCA differs from the median population MCA.

  • Multiple of the Median (MoM) = Doppler MCA peak systolic velocity / MoM 1 (Median)

The MCA peak systolic velocity increases by 0.2 cm/s with every 100g (3.5 ounces) of fetal weight gain.

An increased velocity of blood flow through the middle cerebral artery (and/or dilatation) may be indicative of hypoxia, with a redirection of blood flow to vital organa, such as brain, heart and lungs.

The risk of fetal anemia is highest at observed peak systolic velocities of 1.5 times the median or higher.

There are several indications to be respected, to obtain an accurate measurement during the Doppler:

  • The MCA must occupy more than 50% of the enlarged image;
  • The MCA must be sampled 2mm after internal carotid artery origin;
  • The angle between the ultrasound beam and the direction of blood flow should be 0 degrees.
 

References

Original reference

Mari G, Deter RL, Carpenter RL, et al. Noninvasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization. Collaborative Group for Doppler Assessment of the Blood Velocity in Anemic Fetuses. N Engl J Med. 2000; 342(1):9-14.

Other references

Zimmerman R, Carpenter RJ Jr, Durig P, Mari G. Longitudinal measurement of peak systolic velocity in the fetal middle cerebral artery for monitoring pregnancies complicated by red cell alloimmunisation: a prospective multicentre trial with intention-to-treat. BJOG. 2002;109(7):746-752.

Mari G. Middle cerebral artery peak systolic velocity: is it the standard of care for the diagnosis of fetal anemia?. J Ultrasound Med. 2005; 24(5):697-702.

Delle Chiaie L, Buck G, Grab D, Terinde R. Prediction of fetal anemia with Doppler measurement of the middle cerebral artery peak systolic velocity in pregnancies complicated by maternal blood group alloimmunization or parvovirus B19 infection. Ultrasound Obstet Gynecol. 2001; 18(3):232-236.


Specialty: Obstetrics Gynecology

System: Reproductive

Objective: Screening

Year Of Study: 2000

Abbreviation: MCA

Article By: Denise Nedea

Published On: July 30, 2020

Last Checked: July 30, 2020

Next Review: July 30, 2025