What are the different Doppler (Doppler ultrasound) abnormalities in fetal growth restriction (FGR)?

Doppler Abnormalities in Fetal Growth Restriction (FGR)

The progression of Doppler abnormalities in fetal growth restriction follows a predictable pattern that reflects worsening placental dysfunction and fetal compromise, with umbilical artery abnormalities typically occurring first, followed by middle cerebral artery changes, and finally ductus venosus abnormalities which represent advanced fetal compromise and significantly increased risk of perinatal mortality. 1

Umbilical Artery Doppler Abnormalities

• Umbilical artery Doppler is the primary and most validated Doppler assessment in FGR, with abnormalities reflecting increased impedance to flow in the umbilical circulation due to placental disease 2
• Progression of umbilical artery Doppler abnormalities follows a sequence of increasing severity:
  • Increased resistance: elevated pulsatility index (PI) or systolic/diastolic (S/D) ratio >95th percentile for gestational age 1
  • Decreased end-diastolic velocity: further elevation of flow ratios 1
  • Absent end-diastolic velocity (AEDV): indicates significant placental compromise 1
  • Reversed end-diastolic velocity (REDV): represents severe placental dysfunction and is associated with high perinatal mortality 1
• Umbilical artery Doppler abnormalities are more common in early-onset FGR (diagnosed <32 weeks) compared to late-onset FGR 2
• Abnormal umbilical artery Doppler is associated with a 38% reduction in perinatal mortality when used to guide management 1

Middle Cerebral Artery (MCA) Doppler Abnormalities

• MCA is the largest vessel of the fetal cerebral circulation, carrying approximately 80% of cerebral blood flow 1
• Decreased MCA pulsatility index (<5th percentile) indicates cerebral vasodilation, representing the "brain-sparing effect" in response to hypoxemia 1, 3
• MCA abnormalities are more commonly seen in late-onset FGR (≥32 weeks) 2
• A low MCA pulsatility index is associated with adverse perinatal outcomes in late FGR, with a relative risk of 2.2 (95% CI, 1.5-3.2) for composite adverse outcomes 3
• The cerebroplacental ratio (CPR) or umbilicocerebral ratio (UCR) combines information from both umbilical and cerebral circulation, with abnormal values having stronger associations with adverse outcomes than either vessel alone 3

Ductus Venosus Doppler Abnormalities

• Ductus venosus Doppler abnormalities reflect an advanced stage of fetal compromise and are associated with significantly increased perinatal morbidity and mortality 1
• Progression of abnormalities includes:
  • Increased pulsatility index in the ductus venosus
  • Absent A-wave: associated with odds ratio for stillbirth of 11.16 (95% CI, 6.31-19.73) and 20% frequency of stillbirth 1
  • Reversed A-wave: indicates severe cardiac compromise with 46% risk of stillbirth 1
• Ductus venosus abnormalities primarily reflect increased central venous pressure from right ventricular end-diastolic pressure elevation and decreased cardiac muscle compliance 1
• Even in pregnancies with AEDV/REDV of the umbilical artery, late Doppler abnormalities of the ductus venosus are noted in only about 41% of fetuses 1
• After 32 weeks gestation, abnormal cardiotocography findings will almost invariably precede ductus venosus Doppler abnormalities 1

Aortic Isthmus Doppler Abnormalities

• Retrograde flow in the aortic isthmus is associated with higher rates of perinatal morbidity and mortality 4
• Abnormal aortic isthmus flow patterns typically develop approximately 15-20 days after umbilical and middle cerebral artery Doppler abnormalities 4
• Aortic isthmus abnormalities precede ductus venosus flow deterioration by approximately 3-7 days 4

Uterine Artery Doppler Abnormalities

• Bilateral abnormalities of maternal uterine artery Doppler flow are associated with adverse perinatal outcomes including cesarean delivery, FGR, preterm delivery, and low Apgar scores 1
• Abnormal uterine artery Doppler at the time of FGR diagnosis is associated with higher risk of developing abnormal fetal brain Doppler indices and adverse perinatal outcomes 1
• Uterine artery Doppler is more useful as a screening tool in high-risk pregnancies than in low-risk populations 1

Clinical Implications and Surveillance

• When umbilical artery AEDV is detected, Doppler assessment should be performed 2-3 times per week due to potential for deterioration to REDV 1
• In the setting of REDV, hospitalization, antenatal corticosteroids, and heightened surveillance with cardiotocography at least 1-2 times per day should be considered 1
• The presence of abnormal umbilical artery Doppler combined with structural abnormalities significantly increases the likelihood of chromosomal abnormalities, including trisomy 18 5
• The combination of computerized cardiotocography and ductus venosus Doppler improves outcomes in early-onset FGR, with 95% of surviving infants having normal neurodevelopmental outcomes at 2 years 2

Pitfalls and Caveats

• Doppler abnormalities of the ductus venosus with normal umbilical artery Doppler suggest alternative pathophysiology, possibly related to fetal cardiac, vascular, or genetic abnormalities rather than placental disease 1
• There are currently no randomized trials with adequate sample size to inform recommendations regarding the optimal frequency of umbilical artery Doppler for FGR surveillance 1
• While middle cerebral artery Doppler abnormalities are associated with adverse outcomes in late FGR, there is insufficient evidence supporting its use to determine the timing of delivery 2
• Caution is urged when extrapolating findings from European trials (like TRUFFLE) to practice in the United States, as different monitoring techniques may be used 1