In brief — the direct answer
Uterine artery Doppler assesses resistance in blood flow supplying the uterus and placenta. It can contribute to a combined assessment of pre-eclampsia and placental growth-restriction risk. An elevated pulsatility index is a risk marker, not proof of placental failure or a prediction that a complication will occur. It differs from Doppler of the baby’s umbilical or brain arteries.
What is Uterine Artery Doppler?
The uterine arteries are the primary blood vessels providing nutrients and oxygen to the pregnancy. Early in a healthy pregnancy, these arteries undergo significant changes, transforming from high-resistance narrow vessels into low-resistance wide vessels to accommodate the growing needs of the baby. This process is called 'remodeling.'
If this remodeling does not occur correctly, the blood flow remains 'restricted' or 'turbulent.' Uterine Artery Doppler measures the 'Pulsatility Index' (PI) of this flow. A high PI indicates that the placenta may not be receiving an optimal blood supply. At the MFM Unit, we analyze these Doppler waveforms with extreme precision during the 12-week and 20-week scans to provide an early warning system for placental complications.
Who is at risk?
Use depends on the screening model and local pathway. Prior pre-eclampsia, hypertension, kidney disease, diabetes, autoimmune disease and multiple pregnancy may increase risk. Screening should be discussed alongside history, standardised blood pressure and available biomarkers, rather than offering a Doppler measurement as a stand-alone diagnosis.
How we diagnose it
The assessment is performed during your routine ultrasound appointments (typically at 11–14 weeks and again at 20–22 weeks).
The Procedure:
- Color Mapping: The sonographer or subspecialist uses 'Color Doppler' to locate the uterine arteries where they cross the external iliac arteries.
- Waveform Analysis: We place a 'sample gate' over the vessel to record the speed and pattern of the blood flow.
- PI Calculation: The machine calculates the Pulsatility Index. We also look for the presence of a 'diastolic notch'—a specific shape in the wave that indicates high resistance.
- Combined Assessment: In the first trimester, these Doppler values are combined with your blood pressure (MAP) and placental proteins (PlGF) to generate a personalized risk ratio for pre-eclampsia.
What does management involve?
The responsible clinician combines the result with the other risk factors to decide whether aspirin and additional growth surveillance are indicated. An isolated high PI does not automatically prescribe a particular dose. If aspirin is appropriate, confirm the dose, timing and contraindications with the prescriber. Later abnormal results can still inform surveillance; they should not be interpreted using a first-trimester model outside its validated window.
What are the outcomes?
A risk assessment can guide prevention and surveillance, but neither a normal nor abnormal Doppler guarantees the outcome. Continue routine maternity care and report pre-eclampsia symptoms or reduced movements promptly.
When to see a subspecialist
Arrange review if the result is elevated, if you have a relevant history, or if you are unsure what surveillance was recommended. Severe headache, visual symptoms, upper abdominal pain or sudden breathlessness needs urgent maternity assessment rather than waiting for a screening appointment.