MCA Calculator
Calculate Middle Cerebral Artery peak systolic velocity for fetal anemia risk assessment
⚠️ Medical Disclaimer: This calculator is for informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before making health-related decisions.
About MCA Calculator
The Middle Cerebral Artery (MCA) Calculator is a specialized prenatal diagnostic tool used by obstetricians and perinatologists to assess fetal well-being during pregnancy. This calculator measures the peak systolic velocity of blood flow through the fetal middle cerebral artery and compares it to expected values for gestational age, helping identify fetuses at risk for anemia and other complications.
What is MCA?
The Middle Cerebral Artery (MCA) is one of the three major blood vessels supplying the fetal brain with oxygenated blood. During pregnancy ultrasounds, the MCA is highly visible and accessible for Doppler velocity measurements. When a fetus experiences hypoxia (low oxygen levels), the body prioritizes blood flow to vital organs like the brain, heart, and lungs, resulting in increased blood velocity through the MCA.
How MCA Doppler Works
MCA Doppler ultrasound uses the Doppler effect to measure the velocity of red blood cells moving through the middle cerebral artery. The peak systolic velocity (PSV) represents the maximum blood flow speed during the heart's contraction phase. This measurement is then compared to established median values for the specific gestational age to calculate the Multiples of Median (MoM).
Clinical Applications
- Fetal Anemia Detection: The primary use is identifying fetuses with moderate to severe anemia, particularly from Rh incompatibility or parvovirus B19 infection.
- Growth Restriction Monitoring: Assessing fetuses with intrauterine growth restriction (IUGR) for signs of hypoxia and brain-sparing blood flow redistribution.
- Preeclampsia Risk: Evaluating blood flow patterns in pregnancies complicated by preeclampsia or eclampsia.
- Multiple Pregnancy Complications: Monitoring twin-to-twin transfusion syndrome and other complications in multiple pregnancies.
- Non-invasive Screening: Replacing invasive procedures like amniocentesis or cordocentesis for anemia assessment.
Understanding MCA MoM Values
The MCA MoM (Multiples of Median) value indicates how the measured peak systolic velocity compares to the expected median for that gestational age. A MoM value of 1.0 means the measurement is exactly at the median. Values <1.5 are generally considered normal, while MoM ≥1.5 indicates increased risk of fetal anemia requiring further evaluation and possible intervention such as intrauterine blood transfusion.
The Mari Formula
This calculator uses the validated Mari et al. (2000) formula to calculate expected MCA PSV based on gestational age: Median PSV = e^(2.31 + 0.04643 × GA), where GA is gestational age in weeks (including fractional days). This exponential model has been extensively validated across diverse populations and remains the gold standard for MCA Doppler interpretation in prenatal care. The formula is applicable from 16 to 40 weeks of gestation.
Proper MCA Doppler Technique
Accurate MCA Doppler measurements require proper technique. The fetus should be at rest with no breathing or body movements. Use an axial view of the fetal head to identify the Circle of Willis. The sample volume should be approximately 2mm, placed at the origin of the MCA from the internal carotid artery. Angle correction must be 0° - the ultrasound beam must be parallel to blood flow direction. Obtain at least 3 measurements and record the highest peak systolic velocity.
Clinical Accuracy and Limitations
MCA Doppler has 100% sensitivity for detecting moderate to severe fetal anemia when MoM ≥1.5. The false positive rate is approximately 12% in the general population. However, this false positive rate increases significantly after 35 weeks of gestation, requiring careful clinical correlation. Serial measurements and integration with other clinical findings improve diagnostic accuracy.
When to Perform MCA Doppler
MCA Doppler ultrasound is indicated for evaluating fetal anemia in cases of red blood cell alloimmunization (Rh disease), twin-to-twin transfusion syndrome (TTTS), twin anemia-polycythemia sequence (TAPS), alpha-thalassemia, parvovirus B19 infection, and fetomaternal hemorrhage. It is typically performed starting from 16-18 weeks of gestation when there are risk factors for fetal anemia. Serial measurements may be performed weekly or biweekly depending on risk level and previous results.
This calculator provides immediate MCA MoM results for educational and clinical reference purposes. MCA Doppler interpretation requires proper ultrasound technique, clinical context, and should only be performed and interpreted by qualified healthcare professionals. Always consult obstetricians or perinatologists for medical diagnosis and treatment decisions.
Frequently Asked Questions
MCA Doppler ultrasound measures blood flow velocity in the fetal middle cerebral artery to assess fetal well-being and detect anemia. It's used to evaluate fetuses at risk from Rh incompatibility, parvovirus infection, twin-to-twin transfusion syndrome, alpha-thalassemia, and fetomaternal hemorrhage. The test is performed from 16-40 weeks of gestation.
MCA MoM (Multiples of Median) compares the measured MCA peak systolic velocity to the expected median value for gestational age. It's calculated as: MoM = Observed PSV / Median PSV, where Median PSV = e^(2.31 + 0.04643 × GA). A MoM ≥1.5 indicates high risk of fetal anemia with 100% sensitivity.
MCA MoM ≥1.5 indicates high risk of moderate to severe fetal anemia and requires further evaluation. This threshold has 100% sensitivity for detecting moderate to severe anemia. Values below 1.5 are considered normal with low risk. The false positive rate is approximately 12%, increasing after 35 weeks gestation.
MCA Doppler is performed when there's risk of fetal anemia from Rh incompatibility, parvovirus B19 infection, twin-to-twin transfusion syndrome, alpha-thalassemia, or fetomaternal hemorrhage. It's typically done from 16-40 weeks of gestation during routine prenatal ultrasounds when risk factors are present.
Elevated MCA peak systolic velocity occurs when the fetus experiences hypoxia (low oxygen). The body redirects blood flow to vital organs like the brain, increasing blood velocity. Causes include fetal anemia, Rh disease, parvovirus infection, growth restriction, and placental insufficiency.
MCA Doppler is highly accurate for detecting moderate to severe fetal anemia, with sensitivity of 100% when MoM ≥1.5. The false positive rate is approximately 12%, though this increases after 35 weeks gestation. It's non-invasive and preferred over amniocentesis or cordocentesis for anemia screening.
Yes, this calculator uses the validated Mari et al. (2000) formula: Median PSV = e^(2.31 + 0.04643 × GA). However, it's for educational purposes only. MCA Doppler requires proper ultrasound technique (0° angle correction, fetus at rest, sample at MCA origin) and should only be performed and interpreted by qualified healthcare professionals.
Reviewed by: Health & Nutrition Research Team
Last updated: December 2025