Understanding a Fetal Doppler Report: Which Blood Vessels are Checked?
A Fetal Doppler scan provides valuable information about blood circulation between the mother, placenta and developing baby. However, when expectant parents see terms such as uterine artery, umbilical artery, MCA, PI or RI in the report, they may find them difficult to understand.
Each blood vessel examined during a Fetal Doppler scan answers a different clinical question. Some vessels provide information about blood reaching the placenta, while others help doctors assess placental resistance and how the baby may be responding.
In this article, we explain the main vessels assessed during Fetal Doppler ultrasound and what their findings may indicate.
Watch our video on: Fetal Doppler Scan Check During Pregnancy?
Fetal Doppler Examines a Circulation Pathway
The baby depends on an interconnected circulation pathway:
Mother → Placenta → Umbilical cord → Baby
A Doppler examination may assess different points along this pathway.
- The uterine arteries provide information about maternal blood flow towards the placenta.
- The umbilical artery helps assess resistance within the placental circulation.
- The middle cerebral artery provides information about circulation in the baby’s brain.
- The ductus venosus may be assessed in selected high-risk pregnancies.
The doctor decides which vessels need to be examined based on gestational age, fetal growth, maternal health and the reason for the scan.
1. Uterine Artery Doppler: Mother to Placenta
The uterine arteries are maternal blood vessels that supply blood to the uterus and placenta.
A uterine artery Doppler evaluates how easily blood is moving towards the placenta. The report may contain separate measurements for the left and right uterine arteries, followed by a calculated mean value.
What does it help doctors assess?
Uterine artery Doppler may provide information about:
- Resistance to maternal blood flow
- Placental development and circulation
- The possibility of placental insufficiency
- Risk assessment in pregnancies requiring closer monitoring
A low-resistance pattern generally indicates that blood is flowing more easily towards the placenta. Increased resistance may prompt the doctor to consider the complete pregnancy history, blood pressure, fetal growth and other scan findings.
A single Doppler value should never be interpreted independently.
2. Umbilical Artery Doppler: Placenta to Baby
The umbilical cord connects the baby to the placenta. It contains blood vessels responsible for carrying blood between the baby and the placenta.
The umbilical artery Doppler is one of the most important assessments when there is concern about fetal growth or placental function.
What does the umbilical artery show?
It helps doctors understand the resistance encountered by blood as it travels through the placental circulation.
When placental circulation is functioning appropriately, forward blood flow is generally maintained during both the pumping and resting phases of the baby’s heartbeat.
If placental resistance increases, changes may become visible in the Doppler waveform.
Terms that may appear in the report
An umbilical artery section may mention:
- Normal forward flow
- Increased resistance
- Reduced end-diastolic flow
- Absent end-diastolic flow
- Reversed end-diastolic flow
Absent or reversed end-diastolic flow can be an important finding requiring specialist assessment and close monitoring. The clinical decision depends on gestational age, fetal growth, other Doppler findings and the overall condition of the baby.
An umbilical artery Doppler can help doctors assess whether a small baby may need more frequent surveillance. RCOG
3. Middle Cerebral Artery Doppler: Circulation in the Baby’s Brain
The middle cerebral artery, commonly abbreviated as MCA, is a major blood vessel supplying the baby’s brain.
MCA Doppler is performed by carefully obtaining a blood-flow waveform from this vessel.
Why is the MCA assessed?
MCA Doppler may help doctors evaluate:
- Blood-flow resistance in the baby’s brain
- How the baby may be adapting to changes in placental circulation
- The possibility of fetal anaemia in selected high-risk pregnancies
When placental function is affected, the baby may redistribute blood towards vital organs, particularly the brain. Doctors may identify this adaptation through changes in the MCA Doppler pattern.
MCA peak systolic velocity may also be used when fetal anaemia is suspected. It measures how quickly blood is travelling through the artery. ISUOG
MCA findings must be interpreted according to gestational age and the reason for performing the examination.
4. Cerebroplacental Ratio
The cerebroplacental ratio, also called the CPR, compares the MCA Doppler measurement with the umbilical artery measurement.
Instead of examining only one vessel, CPR helps doctors consider circulation in the placenta and the baby’s brain together.
A CPR value may provide additional information about how the baby is adapting to placental circulation. It is interpreted along with:
- Estimated fetal weight
- Growth pattern
- Amniotic fluid
- Umbilical artery Doppler
- MCA Doppler
- Gestational age
- Other fetal well-being assessments
The CPR should not be interpreted using a single universal cut-off without considering gestational age and the reference chart used by the reporting centre.
5. Ductus Venosus Doppler
The ductus venosus is a small fetal blood vessel that directs oxygen-rich blood towards the baby’s heart.
It is not necessarily checked during every routine Fetal Doppler scan. Doctors may assess it in selected high-risk situations when more detailed information about fetal circulation and cardiac function is required.
Ductus venosus findings are usually interpreted by a fetal medicine specialist together with other Doppler and ultrasound findings.
What Do PI, RI and S/D Mean?
A Fetal Doppler report may contain several abbreviations.
Pulsatility Index
The Pulsatility Index or PI represents variation in blood-flow velocity during the heartbeat. It is commonly used when reporting Doppler findings.
Resistance Index
The Resistance Index or RI is another calculated value used to describe resistance within a blood vessel.
Systolic/Diastolic Ratio
The S/D ratio compares blood-flow velocity during the pumping phase of the heartbeat with velocity during the resting phase.
These values are compared with gestational-age-specific reference ranges. A number appearing high or low cannot be interpreted correctly without knowing:
- Which vessel was examined
- The gestational age
- The quality of the waveform
- The reference chart being used
- Other ultrasound findings
Why Do Different Vessels Show Different Results?
It is possible for one Doppler measurement to be normal while another shows a change. This is because every vessel represents a different part of maternal or fetal circulation.
For example:
- Uterine arteries reflect blood flow from the mother towards the placenta.
- The umbilical artery reflects resistance in placental circulation.
- The MCA reflects circulation within the baby’s brain.
- The ductus venosus provides information related to fetal cardiac circulation.
Doctors therefore look at the complete pattern, not one isolated number.
What Happens When a Doppler Finding Is Abnormal?
An abnormal Doppler finding does not automatically mean that immediate delivery is required.
Depending on the vessel involved, severity and gestational age, the doctor may recommend:
- A repeat Doppler examination
- More frequent growth scans
- Amniotic fluid assessment
- Monitoring the baby’s heartbeat
- Biophysical Profile or BPP
- Maternal blood-pressure monitoring
- Review by a fetal medicine specialist
- Hospital observation in selected cases
- Delivery when remaining inside the womb is considered riskier for the baby
The timing of delivery is an individual medical decision based on the entire clinical picture.
Can Parents Interpret a Fetal Doppler Report Themselves?
Online reference ranges should not be used to diagnose a problem from a Doppler report.
Normal values change with gestational age, and measurements must be obtained using the correct technique. Results also need to be considered alongside fetal growth, amniotic fluid, maternal health and previous scan findings.
Always discuss the report with your obstetrician or fetal medicine specialist.
Fetal Doppler Assessment at Nisarga Diagnostics
At Nisarga Diagnostics, Sanjaynagar, Bangalore, pregnancy ultrasound services include growth and Doppler assessments based on the referring doctor’s recommendation.
Our radiologists are Fetal Medicine Foundation-certified, and pregnancy scans are performed using evidence-based protocols with careful attention to maternal and fetal well-being. Nisarga Diagnostics
Depending on the clinical requirement, the examination may include:
- Fetal growth measurements
- Estimated fetal weight
- Amniotic fluid assessment
- Placental evaluation
- Uterine artery Doppler
- Umbilical artery Doppler
- Middle cerebral artery Doppler
- Cerebroplacental ratio
- Additional fetal well-being assessment
Conclusion
A Fetal Doppler report may contain measurements from the uterine arteries, umbilical artery, middle cerebral artery and, in selected cases, the ductus venosus.
Each vessel answers a different question about maternal, placental or fetal circulation. Doctors combine these findings with fetal growth, amniotic fluid, gestational age and maternal health before recommending further care.
Do not worry based on an isolated value in the report. Discuss the complete findings with your obstetrician or fetal medicine specialist.
This article is intended for patient education and does not replace individual medical consultation.
Founder of Nisarga Diagnostics, is a renowned fetal ultrasound specialist with over 20 years of expertise. An alumnus of Government Medical Colleges in Mysore and Bangalore, he also holds a D.N.B. from the National Board of Examinations, Delhi, and certification from the Fetal Medicine Foundation, London. A former Professor and HOD, he has trained countless PG students and junior radiologists, shaping the future of fetal imaging in India.