How do you interpret fetal Doppler studies?

How to Interpret Fetal Doppler Studies

Fetal Doppler interpretation requires systematic assessment of specific vessels—umbilical artery, middle cerebral artery, and ductus venosus—with each vessel providing distinct information about placental function, fetal cerebral perfusion, and cardiac status that directly predicts perinatal morbidity and mortality. 1

Umbilical Artery Doppler: Primary Assessment of Placental Function

Normal Findings

• Normal umbilical artery flow demonstrates continuous forward flow throughout the cardiac cycle with persistent end-diastolic velocity, established by 14 weeks of gestation 2
• Measure at the abdominal cord insertion (preferred location) when no fetal breathing is present 1
• Normal values are pulsatility index (PI), resistive index (RI), or systolic-to-diastolic (S/D) ratio below the 95th percentile for gestational age 2

Abnormal Findings and Clinical Significance

• Decreased end-diastolic flow (PI >95th percentile) represents the earliest stage of placental compromise 2
• Absent end-diastolic flow (AEDF) indicates severe placental insufficiency with obliteration of approximately 70% of placental tertiary villi arteries 2
• Reversed end-diastolic flow (REDF) is the most severe abnormality, linked to stillbirth and neurological impairment 1
• When umbilical artery Doppler is abnormal in suspected IUGR, it reduces perinatal deaths (RR 0.71), cesarean deliveries (RR 0.90), and inductions of labor (RR 0.89) compared to not using Doppler 1

Critical Pitfall

Do not assume normal umbilical artery flow excludes placental insufficiency in late-onset growth restriction—15-20% of late-onset growth-restricted fetuses with normal umbilical artery Doppler show cerebral vasodilation on middle cerebral artery assessment 2

Middle Cerebral Artery Doppler: Assessment of Fetal Brain Perfusion

Normal Findings

• Measure at the proximal portion of the vessel immediately near the circle of Willis at 0-degree angle of incidence (30-degree angle acceptable) 1
• Normal flow shows moderate diastolic flow with PI values within normal range for gestational age 1

Abnormal Findings: Brain-Sparing Reflex

• Increased end-diastolic flow (decreased PI) indicates fetal hypoxemia with central redistribution of blood flow to the brain, heart, and adrenal glands 1
• This "brain-sparing reflex" is linked to neonatal acidosis and neurological impairment 1
• Calculate the cerebroplacental ratio (MCA PI/umbilical artery PI)—a ratio <5th percentile for gestational age indicates brain sparing 1

Special Application: Fetal Anemia Detection

• Middle cerebral artery peak systolic velocity (MCA-PSV) >1.5 multiples of the median (MoM) predicts moderate or severe fetal anemia 1, 3
• This measurement has revolutionized management of red blood cell isoimmunization, replacing serial amniocentesis 4, 3
• In twin-to-twin transfusion syndrome, donor MCA-PSV >1.5 MoM and recipient MCA-PSV <0.8 MoM diagnoses twin anemia-polycythemia sequence (TAPS) 1

Ductus Venosus Doppler: Assessment of Cardiac Function

Normal Findings

• Normal ductus venosus shows continuous forward flow throughout the cardiac cycle with a biphasic waveform pattern 5
• Identify using color Doppler showing aliasing where the ductus venosus branches from the umbilical vein at the diaphragm level 1, 5
• First peak corresponds to ventricular systole, second peak during passive filling in diastole, followed by a nadir during atrial contraction (A-wave) 1

Abnormal Findings and Urgent Clinical Implications

• Decreased, absent, or reversed flow in the A-wave during atrial contraction represents myocardial impairment and increased ventricular end-diastolic pressure from elevated right ventricular afterload 1, 5
• This abnormal waveform is directly linked to neonatal acidemia and perinatal mortality in growth-restricted fetuses 1, 5
• Abnormal A-wave flow represents late-stage cardiovascular compromise requiring urgent clinical decision-making 5

Critical Technical Pitfall

The most frequent error is mistaking the inferior vena cava for the ductus venosus—proper identification requires color Doppler showing aliasing at the branching site from the umbilical vein 1, 5

Umbilical Vein Doppler: Late-Stage Cardiac Decompensation

Normal Findings

• Normal umbilical vein flow is non-pulsatile and continuous 6

Abnormal Findings: Imminent Fetal Demise

• Pulsatility in the umbilical vein represents transmission of right atrial pressure changes backward through the ductus venosus, signaling advanced cardiac dysfunction and increased central venous pressure 6
• This is a late-stage finding indicating impending fetal decompensation with high risk of imminent fetal demise if delivery is not expedited 6
• Delivery should occur within 24-48 hours of detection 6

Management Algorithm for Umbilical Vein Pulsatility

• Hospitalize immediately 6
• Administer antenatal corticosteroids if <33 6/7 weeks or between 34 0/7-36 6/7 weeks without prior course 6
• Initiate cardiotocography monitoring at least 1-2 times daily 6
• Administer magnesium sulfate for neuroprotection if <32 weeks 6
• Notify neonatal team immediately 6
• If ≥30 weeks: deliver after 24 hours of corticosteroids but not beyond 48 hours 6
• If <30 weeks: balance extreme prematurity risks against imminent fetal demise risk, typically deliver within 24-48 hours 6

Uterine Artery Doppler: Maternal-Placental Interface Assessment

Normal Findings

• Progressive decrease in impedance with advancing gestational age 1
• Measure as the vessel crosses the hypogastric artery before dividing into uterine and cervical branches 1

Abnormal Findings

• Notching or elevated PI in the second trimester is linked to prediction of IUGR 1
• In high-risk women, increased RI (≥0.58 or ≥90th percentile) has a positive likelihood ratio of 10.9 for severe IUGR 1
• However, uterine artery Doppler is not recommended as a screening tool due to inconsistent evidence and lack of standardized criteria 1

Clinical Application Algorithm

For Suspected IUGR (≥23 weeks)

1. Start with umbilical artery Doppler 1

   • If normal: consider serial assessments every 1-2 weeks initially, then every 2-4 weeks if remains normal 2
   • If decreased end-diastolic flow: increase surveillance frequency
   • If AEDF or REDF: proceed to step 2

2. Add middle cerebral artery Doppler 1

   • Calculate cerebroplacental ratio
   • If brain-sparing present: enhanced fetal surveillance required

3. Add ductus venosus Doppler when umbilical artery shows AEDF or REDF 1, 5

   • If A-wave abnormal: intensive surveillance, consider delivery
   • If A-wave normal: continue enhanced surveillance

4. Check for umbilical vein pulsatility in severely compromised fetuses 6

   • If present: deliver within 24-48 hours

For Suspected Fetal Anemia

• Measure MCA peak systolic velocity with angle correction at ≤30 degrees 1
• If MCA-PSV >1.5 MoM: moderate to severe anemia likely, consider invasive testing or intrauterine transfusion 1, 3

Screening Recommendations

• Do not use umbilical artery or uterine artery Doppler for routine screening in low-risk pregnancies—no evidence of benefit 1
• Doppler should only be used in high-risk pregnancies or when IUGR is already suspected 1, 3