Identify fetal anaemia early
MCA PSV is a highly accurate predictor of moderate‑to‑severe fetal anaemia – with a sensitivity of over 90%. It is the standard of care for monitoring Rh disease and other causes of fetal anaemia.
The middle cerebral artery (MCA) is the largest artery supplying blood to the fetal brain. Doppler assessment of the MCA measures the peak systolic velocity (PSV) and the pulsatility index (PI) – providing a non‑invasive estimate of fetal anaemia and detecting the "brain‑sparing" effect that occurs when the fetus is hypoxic. This makes MCA Doppler an essential tool in managing Rh isoimmunisation, fetal growth restriction (IUGR), and other high‑risk conditions.
MCA Doppler is typically performed from the second trimester onwards, often in conjunction with umbilical artery Doppler and other fetal assessments. It is the gold standard for non‑invasive monitoring of fetal anaemia – particularly in Rh disease, where MCA PSV guides the need for intrauterine transfusion. It also helps identify the redistribution of cardiac output to preserve brain oxygenation in fetuses with placental insufficiency.
At Amytri, our MCA Doppler examinations are performed by a consultant radiologist with advanced training in fetal medicine. We use high‑resolution ultrasound and colour Doppler to locate the MCA, obtain accurate velocity waveforms, and calculate the PSV and PI. Our reports are interpreted in the context of your clinical history and gestational age, guiding timely decisions about further monitoring, medical therapy, or delivery.
MCA Doppler is a sensitive and specific tool that tells us how the fetus is responding to challenges – and when it's time to intervene.
MCA PSV is a highly accurate predictor of moderate‑to‑severe fetal anaemia – with a sensitivity of over 90%. It is the standard of care for monitoring Rh disease and other causes of fetal anaemia.
In growth restriction, MCA PI reflects the brain‑sparing effect – a low PI indicates redistribution to preserve cerebral oxygenation. Progressive changes signal the need for delivery, even before umbilical artery Doppler becomes abnormal.
MCA Doppler‑guided interventions – from intrauterine transfusion to timely delivery – have been shown to reduce the risk of neonatal anaemia, brain injury, and long‑term neurodevelopmental impairment.
We obtain a high‑quality waveform from the proximal MCA and calculate the indices that guide clinical decisions.
We measure the maximum velocity during systole. An elevated PSV (≥1.5 MoM) indicates fetal anaemia – the higher the PSV, the more severe the anaemia. It is used to time intrauterine transfusion in Rh disease.
MCA PI reflects cerebrovascular resistance. In hypoxia, the fetal brain dilates cerebral vessels to increase blood flow – resulting in a lower PI. This is the "brain‑sparing" effect and is a marker of fetal adaptation to hypoxia.
RI = (S‑D)/S. A low RI also indicates reduced cerebral resistance, consistent with brain‑sparing. It is less used than PI but can be a useful adjunct.
PSV is expressed as MoM, which adjusts for gestational age. An MCA PSV ≥1.5 MoM is the threshold for moderate‑to‑severe anaemia. Serial measurements track the progression of anaemia or the response to treatment.
CPR = MCA PI / Umbilical Artery PI. A low CPR indicates redistribution and is a more sensitive predictor of adverse outcomes in growth restriction – we often calculate this in combination with umbilical artery Doppler.
We combine MCA Doppler with umbilical artery Doppler, fetal biometry, amniotic fluid volume, and biophysical profile to provide a comprehensive assessment of fetal wellbeing.
Your obstetrician refers you for MCA Doppler – often in the context of Rh isoimmunisation, suspected fetal anaemia, or IUGR. We review your history and antibodies if relevant.
We locate the MCA using colour Doppler at its origin from the circle of Willis. We then obtain a spectral Doppler waveform at a 0‑degree insonation angle for accurate PSV measurement.
We measure PSV, PI, and RI. PSV is expressed as MoM. Normal PSV indicates no significant anaemia; elevated PSV (≥1.5 MoM) prompts further evaluation (often intrauterine transfusion in Rh disease). Low PI indicates brain‑sparing and should be correlated with umbilical artery findings.
We provide a detailed Doppler report and discuss the findings with you and your obstetrician. Recommendations may include serial MCA Doppler, intrauterine transfusion, or delivery planning.
It is a key tool in the management of specific high‑risk conditions, particularly those involving the fetus's blood and oxygen supply.
MCA PSV is the standard non‑invasive test to monitor fetal anaemia in Rh‑negative mothers with Rh‑positive babies. It guides the need for intrauterine transfusion.
In IUGR, MCA PI (or the cerebro‑placental ratio) helps assess whether the fetus is compensating for hypoxia – a low PI may indicate brain‑sparing and the need for delivery.
Parvovirus can cause fetal anaemia – MCA Doppler is used to monitor for anaemia and guide intrauterine transfusion if needed.
Conditions like lupus or other autoimmune disorders can cause fetal anaemia – MCA Doppler is recommended for monitoring.
TAPS is a complication of monochorionic twins – MCA Doppler (PSV >1.5 MoM in the donor) is diagnostic and guides management.
When umbilical artery Doppler is abnormal, MCA Doppler and CPR help assess fetal adaptation and guide delivery timing.
MCA Doppler requires careful technique – obtaining the waveform at the correct angle and site is critical for accurate measurement. Our consultant radiologist has extensive experience in fetal Doppler, ensuring reliable PSV and PI values that are essential for clinical decision‑making.
MCA Doppler can be a stressful test – having your partner with you provides support and shared understanding.
We encourage partners to attend. We explain the waveforms and what they indicate, and answer any questions. If the results are abnormal, we discuss them sensitively and provide a clear plan for management – whether it's closer monitoring, intrauterine transfusion, or delivery.
It is a specialised ultrasound that measures blood flow velocity in the fetal middle cerebral artery. It provides information about fetal anaemia (via PSV) and fetal adaptation to hypoxia (via PI).
Yes. It uses standard diagnostic ultrasound with no known harmful effects. The thermal index is kept within safe limits, and it is a routine tool in fetal medicine worldwide.
An MCA PSV ≥1.5 MoM indicates moderate‑to‑severe fetal anaemia. Common causes include Rh disease, parvovirus infection, and TAPS. It often prompts intrauterine transfusion or early delivery.
A low MCA PI suggests the "brain‑sparing" effect – the fetus is redirecting blood flow to preserve brain oxygenation in the face of hypoxia (often due to placental insufficiency). It is a marker of fetal adaptation and may guide delivery timing.
It depends on the indication. In Rh disease, it is performed weekly or every 1‑2 weeks. In IUGR, it is often done with each growth scan (every 2‑4 weeks) to monitor trends.
Yes, typically a referral from your obstetrician is required, especially if you have Rh antibodies or other risk factors. We will work closely with your care team to provide coordinated management.
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