What is the cut off for diagnosing Intrauterine Growth Restriction (IUGR) in an anomaly scan?

Cut-off for Diagnosing IUGR in Anomaly Scan

Intrauterine growth restriction (IUGR) is defined as sonographic estimated fetal weight (EFW) below the 10th percentile for gestational age. 1

Diagnostic Criteria

• IUGR is diagnosed when the EFW is below the 10th percentile for gestational age and/or abdominal circumference (AC) is below the 10th percentile 1
• Severe IUGR is defined as EFW below the 3rd percentile 1
• IUGR should be differentiated from small for gestational age (SGA), as IUGR implies a pathologic process behind the low fetal weight 2, 3

Additional Parameters to Confirm Pathological Growth Restriction

• Abnormal umbilical artery Doppler (pulsatility index, resistance index, or systolic-to-diastolic ratio greater than the 95th percentile for gestational age) 1
• Absent or reversed end-diastolic velocity (AEDV or REDV) in the umbilical artery 1
• Reduced growth velocity (change in AC of <5 mm over 14 days or AC/EFW crossing centiles with >30% reduction) 1
• Oligohydramnios 4

Classification Based on Timing

• Early-onset IUGR: Diagnosed at <32 weeks gestation 1
• Late-onset IUGR: Diagnosed at ≥32 weeks gestation 1

Management After Diagnosis

• Once IUGR is diagnosed, serial umbilical artery Doppler assessment should be performed to assess for deterioration 1

• Initial assessment should occur every 1-2 weeks 1

• If umbilical artery Doppler remains normal after initial assessment, a less frequent interval (every 2-4 weeks) may be considered 1

• For EFW between 3rd-9th percentile with normal umbilical artery Doppler, follow-up should include:

  • Umbilical artery Doppler every 1-2 weeks initially, then every 2-4 weeks if stable 1
  • Cardiotocography (CTG) once per week 1
  • EFW assessment every 3-4 weeks 1

• For severe IUGR (EFW <3rd percentile):

  • Weekly umbilical artery Doppler evaluation 1
  • Weekly CTG 1
  • Consider EFW assessment every 2 weeks 1

Important Considerations

• Umbilical artery Doppler evaluation helps differentiate the hypoxic growth-restricted fetus from the non-hypoxic small fetus, reducing unnecessary interventions 1

• For pregnancies with abnormal umbilical artery Doppler (AEDV/REDV), more intensive monitoring is required:

  • Doppler assessment 2-3 times per week for AEDV 1
  • For REDV, consider hospitalization, antenatal corticosteroids, and daily CTG monitoring 1
  • Hospital admission should be considered if fetal surveillance more often than 3 times per week is deemed necessary 1

• Early-onset IUGR (<32 weeks) may warrant genetic testing:

  • Consider chromosomal microarray analysis (CMA) when IUGR is accompanied by fetal malformations or polyhydramnios 1
  • CMA should be offered for unexplained isolated IUGR diagnosed at <32 weeks gestation (4-10% incremental yield over karyotype) 1

Common Pitfalls to Avoid

• Not distinguishing between IUGR and SGA - IUGR implies a pathologic process and carries higher risks of perinatal morbidity and mortality 2, 5
• Relying solely on EFW without considering Doppler studies - the combination of biometry and Doppler provides better diagnostic accuracy 4
• Inadequate follow-up frequency - early detection of deterioration is crucial for optimizing outcomes 1
• Failure to consider the etiology of IUGR, which can include maternal, placental, fetal, and genetic factors 2, 3