At what gestational age can twin-twin transfusion syndrome (TTTS) be diagnosed?

Earliest Gestational Age for Diagnosis of Twin-Twin Transfusion Syndrome

Twin-twin transfusion syndrome (TTTS) can be diagnosed as early as 16 weeks of gestation, which is when routine ultrasound surveillance for monochorionic diamniotic (MCDA) twin pregnancies should begin. 1

Diagnostic Criteria and Timing

• TTTS diagnosis requires two essential criteria:

  1. Presence of a monochorionic diamniotic pregnancy
  2. Oligohydramnios (maximal vertical pocket ≤2 cm) in one sac with polyhydramnios (maximal vertical pocket ≥8 cm) in the other sac 1, 2

• While most cases are diagnosed in the mid-trimester, TTTS can manifest at any time during gestation, with the mean gestational age at diagnosis being approximately 21-22 weeks 1, 3

• The earliest documented cases in the literature show TTTS being diagnosed as early as 15 weeks of gestation 4, 3

Recommended Surveillance Protocol

• All women with twin pregnancies should have an ultrasound at 10-13 weeks to establish chorionicity 1

• For MCDA pregnancies, ultrasound surveillance should:

  • Begin at 16 weeks of gestation 1, 2
  • Continue at least every 2 weeks until delivery 1
  • Include assessment of amniotic fluid volumes in both sacs and presence of fetal bladders 1

• More frequent monitoring (weekly) is recommended when there are concerning findings such as:

  • Discordant amniotic fluid volumes that don't yet meet TTTS criteria 1
  • Discordant estimated fetal weight (>25% difference) 4
  • Discordant maximum vertical pocket (>65% difference) 4, 5

Clinical Presentation and Natural History

• The presentation of TTTS is highly variable, with most cases diagnosed between 18-28 weeks 1, 6

• Without intervention, advanced TTTS (stages III-IV) has a mortality rate of 70-100% 2, 7, 6

• Even with early diagnosis and treatment, TTTS carries significant risks:

  • 30-50% chance of perinatal mortality despite laser therapy 2
  • 5-20% risk of long-term neurologic impairment in survivors 2, 7

Important Considerations

• First-trimester findings that may indicate increased risk for developing TTTS include:

  • Nuchal translucency abnormalities
  • Crown-rump length discrepancy 1

• Velamentous cord insertion is found in approximately one-third of placentas with TTTS and may be an early risk factor 1

• After 28-30 weeks, new development of TTTS becomes less likely, though monitoring should continue throughout pregnancy 4

• When TTTS is diagnosed, referral to a fetal intervention center is recommended for evaluation and potential fetoscopic laser photocoagulation, particularly for stages II-IV between 16-26 weeks 2

By following the recommended surveillance protocol starting at 16 weeks, clinicians can identify TTTS at its earliest presentation, which is crucial for improving outcomes through timely intervention.