What are the diagnostic criteria for Fetal Growth Restriction (FGR) using Ultrasound (USG) Doppler?

Diagnostic Criteria for Fetal Growth Restriction Using Ultrasound Doppler

FGR is diagnosed when estimated fetal weight (EFW) is below the 3rd percentile, OR when EFW is between the 3rd-10th percentile with abnormal umbilical artery Doppler velocimetry. 1, 2

Initial Diagnostic Assessment

Biometric Criteria

• EFW < 3rd percentile alone establishes FGR diagnosis regardless of Doppler findings 2
• EFW between 3rd-10th percentile requires abnormal Doppler studies to differentiate true FGR from constitutionally small (SGA) fetuses 1, 2
• Fetuses with EFW 3rd-10th percentile and normal Doppler are classified as small for gestational age (SGA), not FGR 2

Essential Doppler Parameters for Diagnosis

Umbilical Artery (UA) Doppler - The most critical diagnostic parameter:

• Pulsatility index (PI) > 95th percentile indicates abnormal placental resistance 2
• Decreased end-diastolic velocity represents early compromise 3
• Absent end-diastolic velocity (AEDV) indicates severe placental dysfunction 4, 3
• Reversed end-diastolic velocity (REDV) represents critical compromise with high perinatal mortality 1, 4
• Management incorporating umbilical artery Doppler reduces perinatal death by 38% 1, 4

Middle Cerebral Artery (MCA) Doppler - Indicates fetal adaptation:

• PI < 5th percentile demonstrates cerebral vasodilation ("brain-sparing effect") 2
• Abnormal MCA Doppler identifies fetuses at risk for adverse perinatal outcome 1
• In late-onset FGR (>32 weeks), MCA abnormalities precede deterioration and stillbirth 3

Cerebroplacental Ratio (CPR):

• PI < 5th percentile indicates redistribution of blood flow favoring the brain 2
• Abnormal CPR combined with abnormal uterine artery Doppler and EFW > 3rd percentile discriminates SGA pregnancies at risk for adverse outcomes 1

Uterine Artery Doppler - Maternal-placental interface:

• Mean PI > 95th percentile indicates inadequate placental perfusion 2
• Abnormal uterine artery Doppler at FGR diagnosis predicts higher risk of abnormal fetal brain Doppler and adverse perinatal outcomes 1, 4

Ductus Venosus (DV) Doppler - Advanced fetal compromise:

• PI > 95th percentile indicates increased central venous pressure 2
• Absent or reversed A-wave flow is associated with neonatal demise 1, 4
• DV abnormalities typically occur after umbilical artery changes and represent advanced stage requiring delivery consideration 4, 3

Diagnostic Algorithm by Gestational Age

Early-Onset FGR (≤32 weeks):

• Diagnosis requires EFW < 10th percentile with abnormal UA Doppler 3
• Progression of UA Doppler abnormality determines clinical acceleration 3
• Abnormal DV Doppler precedes deterioration of biophysical variables and stillbirth 3

Late-Onset FGR (>32 weeks):

• MCA Doppler abnormalities become more predictive than UA alone 3
• CPR is particularly useful for identifying fetuses requiring surveillance 3
• From 34-38 weeks, delivery timing remains controversial; from 38 weeks onward, delivery is favored 3

Critical Diagnostic Pitfalls

Avoid misclassifying constitutionally small fetuses:

• Integrating Doppler with biometry reduces false-positive FGR diagnosis by 52-77% compared to using EFW < 10th percentile alone 2
• Normal Doppler studies with EFW 3rd-10th percentile indicates SGA, not FGR 2

Recognize adapted growth restriction:

• Fetuses with EFW 10th-50th percentile but abnormal Doppler represent "appropriate for gestational age with adapted growth restriction" and require surveillance 2

DV abnormalities with normal UA Doppler:

• This pattern suggests alternative pathophysiology (cardiac, vascular, or genetic abnormalities) rather than placental disease 4
• Requires different diagnostic workup beyond standard FGR evaluation 4

Complementary Diagnostic Studies

Biophysical Profile (BPP):

• Not diagnostic for FGR but essential for fetal well-being assessment once FGR is diagnosed 1
• Abnormal BPP indicates need for delivery consideration 1

Amniotic Fluid Assessment:

• Oligohydramnios (AFI < 5 cm) supports FGR diagnosis and indicates chronic uteroplacental insufficiency 5
• Severe oligohydramnios (AFI ≤ 3 cm) is an independent indication for delivery consideration 5