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MCA Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Bogna Szyk and Jack Bowater
Based on research by
Mari, G., Deter, R. L., Carpenter, R. L., Rahman, F., Zimmerman, R., Moise, K. J., Jr, Dorman, K. F., Ludomirsky, A., Gonzalez, R., Gomez, R., Oz, U., Detti, L., Copel, J. A., Bahado-Singh, R., Berry, S., Martinez-Poyer, J., Blackwell, S. C. 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.; The New England journal of medicine; January 2000See 2 more sources
Mari, G., Abuhamad, A. Z., Cosmi, E., Segata, M., Altaye, M., Akiyama, M. Middle cerebral artery peak systolic velocity: technique and variability; Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine; April 2005Mari, G., Norton, M. E., Stone, J., Berghella, V., Sciscione, A. C., Tate, D., Schenone, M. H. Society for Maternal-Fetal Medicine (SMFM) Clinical Guideline #8: the fetus at risk for anemia--diagnosis and management; American journal of obstetrics and gynecolog; June 2015
Last updated: May 20, 2024

The MCA calculator assesses the risk of fetal anemia in both single and twin pregnancies. Our calculations are based on a Middle Cerebral Artery (MCA) doppler scan, performed during routine pregnancy check ups.

Our calculator will provide you with the median MCA velocity for a given gestational age, the Multiple of Median (MoM) value, and the full meaning of said value.

Read on to find out more information on the middle cerebral artery doppler in pregnancy, and the application of a MCA Doppler for fetal anemia. 👇

How to use the MCA calculator?

To take full advantage of the MCA calculator, you'll need the following data:

  1. Gestational age, given in weeks; and
  2. MCA peak systolic velocity, measured during a routine pregnancy check-up (a Fetal Middle Cerebral Artery Doppler ultrasound reading – find more technical details below).

What is MCA?

MCA stands for the Middle Cerebral Artery. It's one of the three biggest vessels supplying the brain with blood, and it's very visible during fetal ultrasounds. Its measurements are used to check the well-being of the child.

What is a Doppler ultrasound?

A Doppler ultrasound is a type of ultrasound technique that allows us to visualize the blood flow and its velocity. We use the movement of red blood cells inside the blood vessels to obtain this data.

Check out our other useful pregnancy calculators!

MCA doppler in perinatology

Perinatology and MCA are long-time friends; doppler ultrasounds are used both for regular check-ups and for more specific, detailed diagnostics. The middle cerebral artery is assessed for a number of reasons:

  • Diagnosis of the growth restriction;

  • Assessment of risk of the preeclampsia, and eclampsia;

  • A suspected parvovirus B-19 infection;

  • Serological ( blood Rh type) conflict: happens when mother is Rh-, and the baby is Rh+; and

  • Complications in multiple pregnancies.

All of the above states result in hypoxia, an inadequate supply of oxygen to the body of the fetus. The fetus's body is trying to protect their most essential organs, such as the brain, heart, and lungs. To achieve this, the baby redirects the blood flow into these organs to obtain the best supply of blood possible.

All these actions result in an increased velocity of the blood flow through the brain's arteries, and their dilatation.

In the most severe cases, the blood flow is so limited that we cannot detect any sign of blood flow inside the brain's blood vessels, as the flow observed during the diastole is retrograde. This state is very serious and requires immediate medical attention.

We also use the ratio between the umbilical artery and the MCA to get a fuller picture of the baby's well-being.

Fetal anemia

Fetal anemia is a condition in which the fetus's red blood cells are destroyed too quickly. The most common reasons in the US for fetal anemia are a parvovirus infection or a RH conflict. 🩸

Fetal anemia can be detected through a biopsy of the umbilical cord or amniotic sac. Still, the preferable, less invasive option is to measure the middle cerebral artery and umbilical artery blood flow. In a more advanced scenario, we can use a regular ultrasound scan to see that the fetus is enlarged and that fluid has collected in different parts of the body – we call it the hydrops fetalis. The consequences of this state may be fatal.

How can we treat fetal anemia?

Intrauterine blood transfusions are a common way to treat fetal anemia. If the pregnancy is advanced and close to the expected due date, we can also perform an elective C-section.

Nevertheless, the best method is to prevent fetal anemia by proper immunization of all Rh- women after every pregnancy or miscarriage. You should also avoid any sources of parvovirus while pregnant.

How to calculate MCA?

The traditional method to calculate the median MCA peak systolic velocity is through medical research. MCA ultrasound measurements are taken at respective weeks of the pregnancy in a group of hundreds or thousands of women. We need to take into account their ethnicity, age, number of fetuses, and weight.

There are a few established rules:

  • With every 100 g (3.5 ounces) gained by the fetus, the MCA peak systolic velocity increases by 0.2 cm/s;

  • Distortion of the ultrasound reading: the peak velocity loses 0.1 cm/s for every 1 degree of beam displacement; and

  • A linear model exists, established in 2000 by Mari et al.: log(MCA PSV)= 2.31 + 0.046 × GA , where MCA PSV = middle cerebral artery peak systolic velocity, and GA = gestation age in weeks.

How to correctly measure the fetal middle cerebral artery?

Performing a correct MCA doppler scan may be quite challenging, especially if you're just at the beginning of your journey – practice as often as you can, following the instructions below:

  1. Find the axial section of the brain using the B scan of the ultrasonograph – choose the place in which you can clearly see the thalami and the cavitas septi pellucidi.
  2. Display the circle of Willis on screen, and measure the peak velocity flow as close to the internal carotid artery as possible.

The angle between the probe beam and the direction of the blood flow should be equal to 0. 📐

Łucja Zaborowska, MD, PhD candidate
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