What are the different types of selective Fetal Growth Restriction (FGR) in multiple gestations?

Types of Selective Fetal Growth Restriction (sFGR) in Multiple Gestations

Selective fetal growth restriction (sFGR) in monochorionic twin pregnancies is classified into three distinct types based on umbilical artery Doppler findings in the growth-restricted twin, each with different prognosis and management implications. 1

Classification of sFGR Types

sFGR is classified into three types based on umbilical artery Doppler findings:

• Type I sFGR: Characterized by constant end-diastolic flow (EDF) in the umbilical artery of the growth-restricted twin 1

  • Has the best prognosis with 96% survival rate 2
  • Most common type, representing approximately 62% of sFGR cases 2

• Type II sFGR: Characterized by constant absent or reversed end-diastolic flow in the umbilical artery of the growth-restricted twin 1

  • Associated with poorest outcomes and highest risk of intrauterine fetal demise 1
  • Survival rate of only 55%, significantly lower than other types 2
  • Independently associated with decreased survival (odds ratio 0.06) 2

• Type III sFGR: Characterized by intermittent absent or reversed end-diastolic flow in the umbilical artery of the growth-restricted twin 1

  • Intermediate prognosis with 83% survival rate 2
  • Associated with higher prevalence of proximate cord insertion (12.8%) compared to other types 3
  • Independently associated with decreased survival (odds ratio 0.21) 2

Diagnostic Criteria for sFGR

According to the Delphi consensus, sFGR in monochorionic twins is diagnosed when either: 4

• One solitary parameter: Estimated fetal weight (EFW) of one twin < 3rd percentile
• OR at least two of the following contributory parameters:
  • EFW of one twin < 10th percentile
  • Abdominal circumference of one twin < 10th percentile
  • EFW discordance ≥ 25%
  • Umbilical artery pulsatility index of the smaller twin > 95th percentile

Clinical Implications and Management Considerations

• Onset timing affects outcomes: Early-onset sFGR (diagnosed at 16-20 weeks) has lower survival (85%) compared to late-onset sFGR (diagnosed at 30 weeks) with 98% survival 2

• Complications: sFGR can coexist with other monochorionic twin complications:

  • 10% develop twin-twin transfusion syndrome (TTTS) 2
  • 3% develop twin anemia-polycythemia sequence (TAPS) 2
  • When sFGR develops TTTS, survival drops significantly to 65% 2

• Placental characteristics: Discordant cord insertions (velamentous-paracentral) are significantly more common in sFGR placentas (45.5%) compared to uncomplicated twin placentas (19.9%) 3

• Type III sFGR is associated with larger arterio-arterial anastomoses (3.0 mm vs. 2.2 mm in other types) 3

Management Approach

Management of sFGR requires close monitoring with:

• Weekly assessment of fetal well-being including Doppler of the umbilical artery and middle cerebral artery 1
• Biweekly fetal biometry evaluations 1
• Consideration of delivery timing based on sFGR type and severity 1
• Consultation with specialized fetal care centers for advanced cases 1

Common Pitfalls and Caveats

• Doppler flow patterns can change over the course of pregnancy, requiring regular reassessment 1
• The presence of a major anomaly significantly worsens prognosis (survival 70% vs. 92% without anomalies) 2
• Birth weight discordance is less severe in sFGR with proximate cord insertion (18.5%) compared to those without (28.0%) 3
• Monitoring should continue even after any fetal intervention 1

Understanding the specific type of sFGR is crucial for appropriate risk stratification, counseling, and management decisions in monochorionic twin pregnancies.