SWARAJ HOSPITAL & RESEARCH INSTITUTE

BOLANGIR, ODISHA  •  OBSTETRICS & GYNAECOLOGY CLINICAL PATHWAY SERIES

Clinician Reference Infographic

Doppler in Obstetrics — Vessels, Waveforms & Clinical Action

Doppler ultrasound measures blood-flow velocity waveforms in maternal and fetal vessels. It shows how well the placenta is working and how the fetus is adapting to stress. It is a targeted test for high-risk pregnancies (growth restriction, hypertension, alloimmunisation, twins) — it is not a routine screen for low-risk women, and it never replaces CTG, growth scans or amniotic fluid assessment.

🎯 WHEN TO USE DOPPLER

Suspected FGR / SGA — estimated fetal weight or abdominal circumference below the 10th centile

Hypertensive disorders — pre-eclampsia, chronic hypertension, or high uterine artery resistance at screening

Red-cell alloimmunisation or suspected fetal anaemia — MCA peak systolic velocity (see our Rh isoimmunization guide)

Twins — selective growth restriction, twin-to-twin transfusion syndrome, TAPS

Other triggers: reduced fetal movements, oligohydramnios, previous stillbirth or severe early-onset pre-eclampsia

Not for routine low-risk screening — universal third-trimester Doppler has not improved outcomes in low-risk women. Follow the ALARA principle and avoid routine spectral Doppler in the first trimester.

📐 READING THE WAVEFORM — THE INDICES

S/D ratio = peak systolic ÷ end-diastolic velocity. RI = (S − D) ÷ S.

PI (pulsatility index) = (S − D) ÷ mean velocity — the most useful index, because it still works when end-diastolic flow is absent or reversed

Compare against gestation-specific centiles — normal values fall as pregnancy advances, so one fixed number does not fit all weeks

Resistance is lower in a healthy placenta: the more diastolic flow, the healthier the downstream bed

🩸 THE KEY VESSELS

Uterine Artery (maternal)

Reflects trophoblast invasion and spiral artery remodelling

Normal: early-diastolic notch disappears by about 24–26 weeks

Raised mean PI or persistent notch → higher risk of pre-eclampsia and FGR

Umbilical Artery (placental)

Reflects placental resistance — the main vessel for FGR surveillance

Measure in a free loop of cord, with no fetal breathing

Raised PI → AEDF → REDF as placental disease worsens

Middle Cerebral Artery (brain)

Normal fetal brain has high resistance

Low PI = brain-sparing (blood redirected to the brain under hypoxia)

PSV > 1.5 MoM suggests moderate–severe fetal anaemia

Ductus Venosus (venous)

Shows how the fetal heart is coping — an late sign of compromise

Normal: forward flow throughout the cardiac cycle

Absent or reversed a-wave = cardiac decompensation

📈 UMBILICAL ARTERY — THE FOUR PATTERNS

Schematic spectral waveforms. Above the line = forward flow; below the line = reversed flow in diastole.

Normal — continuous forward diastolic flow, PI within centile range

Raised PI (> 95th centile) — placental resistance rising; increase surveillance

AEDF — no forward flow in diastole; significant placental insufficiency

REDF — flow reverses in diastole; highest perinatal mortality risk

⏱️ FGR — STAGING AND SURVEILLANCE

Early-onset FGR (before 32 weeks)

Normal UA DopplerRepeat about weekly (often twice weekly if the PI is raised); watch the fetal growth rate

AEDFCloser surveillance (CTG, DV Doppler); consider delivery by about 32–34 weeks if stable

REDFConsider delivery at about 30–32 weeks, earlier if DV or CTG deteriorates

DV a-wave absent/reversed, or abnormal CTG short-term variationDeliver — indicates imminent fetal compromise

Late-onset FGR (after 32 weeks)

UA Doppler is often normal even in a compromised fetus — a normal UA does not reassure on its own

Use MCA PI and the cerebroplacental ratio (CPR = MCA PI ÷ UA PI): a low CPR (below the 5th centile, or < 1) signals redistribution and higher risk of adverse outcome

Consider delivery at about 37 weeks in FGR with abnormal CPR or MCA; timing is individualised

Before delivery under 34 weeks: give antenatal corticosteroids, and magnesium sulphate for neuroprotection when delivery is expected before 32 weeks. See our ACS guide.

🚨 DOPPLER RED FLAGS — ESCALATE THE SAME DAY

Reversed end-diastolic flow in the umbilical artery

Absent or reversed a-wave in the ductus venosus, or pulsatile umbilical vein flow

MCA peak systolic velocity above 1.5 MoM (suspected fetal anaemia) — arrange fetal medicine review for possible intrauterine transfusion

Any abnormal Doppler together with a reduced-variability or decelerating CTG

🔬 MCA PSV FOR FETAL ANAEMIA — THE TECHNIQUE

Start from about 18 weeks in at-risk pregnancies; repeat every 1–2 weeks

Sample the proximal third of the MCA, near its origin from the circle of Willis

Keep the insonation angle as close to 0° as possible; take the highest velocity from several traces

Values are given as multiples of the median (MoM) for gestation; > 1.5 MoM → cordocentesis and transfusion planning

Accuracy falls after about 35 weeks — false positives rise, so interpret with clinical context

✅ TECHNIQUE — GETTING A TRUSTWORTHY TRACE

1

Record during fetal quiescence — no breathing movements, no fetal body movement

2

Keep the insonation angle below 30° (0° for MCA PSV)

3

Use low wall filter, appropriate gain, and the smallest sample volume that covers the vessel

4

Use minimal probe pressure — pressure on the fetal head can change MCA values

5

Take 3 or more similar consecutive waveforms and average them

Memory Aid

DOPPLER

A checklist for every Doppler request, from indication to action.

D

Define the indication — who is this scan for, and why?

O

Optimise settings — quiet fetus, low angle, low wall filter

P

Pick the right vessel — UA, MCA, DV, or uterine artery

P

PI against gestation-specific centiles

L

Look at trends — serial readings tell more than a single value

E

Examine alongside CTG, growth and liquor volume

R

Respond by gestation — steroids, surveillance, or delivery

Remember: a normal Doppler in a late-onset growth-restricted fetus is not the end of surveillance — it only means one pathway is still normal.

Swaraj Hospital & Research Institute · Department of Obstetrics & Gynaecology, Bolangir, Odisha

Clinician-facing summary based on ISUOG and RCOG guidance; centile charts, delivery thresholds and surveillance intervals vary between guidelines and units — follow local protocol and seek fetal medicine advice for abnormal findings.