How is twin anemia polycythemia sequence (TAPS) diagnosed and managed after birth?

Postnatal Diagnosis of Twin Anemia Polycythemia Sequence (TAPS)

Diagnose postnatal TAPS by documenting an intertwin hemoglobin difference ≥8 g/dL or a reticulocyte count ratio >1.7 between the donor and recipient twin, combined with placental injection studies demonstrating exclusively small arteriovenous anastomoses (<1 mm). 1

Diagnostic Criteria

Hematologic Assessment

• Obtain complete blood counts with reticulocyte counts from both twins immediately after birth 1, 2
• The donor twin will demonstrate:
  • Anemia (hemoglobin typically <10 g/dL) 3
  • Markedly elevated reticulocyte count (often >72‰) 2
• The recipient twin will show:
  • Polycythemia (hemoglobin typically >20-22 g/dL) 2, 3
  • Normal or low reticulocyte count 1

Placental Pathology Examination

• Perform color dye injection of the placenta to identify vascular anastomoses 2, 4
• Postnatal TAPS diagnosis requires identification of exclusively minuscule arteriovenous anastomoses (<1 mm diameter) 1
• The presence of larger anastomoses (>1 mm) suggests alternative diagnoses like TTTS 1
• Barium angiography can provide additional detail on placental vascular architecture 4

Clinical Presentation Clues

When twins are born with a "pale and plethoric" appearance, immediately suspect TAPS and initiate diagnostic workup 2. This visual discordance should trigger urgent hematologic evaluation even in dichorionic twins, as rare cases have been reported 2.

Postnatal Management and Surveillance

Immediate Neonatal Care

• The donor twin requires close monitoring for complications of severe anemia including high-output cardiac failure 5, 3
• The recipient twin needs surveillance for polycythemia-related complications including hyperviscosity syndrome and thrombosis 3
• Severe neonatal morbidity occurs in 33% of TAPS-affected twins, with equal risk between donors and recipients 3

Neurologic Evaluation

• Perform cerebral ultrasound on both twins to screen for intracranial hemorrhage and post-hemorrhagic ventricular dilatation 2
• The recipient twin faces particular risk for severe cerebral injury due to polycythemia-induced hyperviscosity 2
• Donor twins may develop brain injury from severe anemia and cardiac compromise 2

Long-Term Follow-Up

• Conduct hearing screening, as TAPS twins have increased risk for hearing loss 2
• Arrange long-term neurodevelopmental follow-up given the high risk of neurodevelopmental impairment 2
• Perinatal mortality in TAPS reaches 15% overall, with donor twins at particularly high risk (22% versus 7% in recipients) 5, 3

Critical Pitfalls to Avoid

Don't Assume Dichorionicity Excludes TAPS

Although TAPS occurs almost exclusively in monochorionic twins, rare cases in dichorionic twins with deep-hidden anastomoses have been documented 2. When confronted with a pale and plethoric dichorionic twin pair, complete the full diagnostic workup including placental injection studies 2.

Don't Delay Placental Examination

Placental pathology with dye injection must be performed promptly after delivery, as this is the only definitive method to confirm the characteristic small anastomoses (<1 mm) that distinguish TAPS from other forms of twin-to-twin transfusion 1, 2.

Don't Overlook Subtle Hematologic Differences

The hemoglobin difference threshold of ≥8 g/dL is critical—smaller differences may represent normal twin variation rather than pathologic transfusion 1. However, when combined with elevated reticulocyte ratios >1.7, even borderline hemoglobin differences warrant serious consideration 1.

Severity Assessment

Postnatal TAPS severity correlates with antenatal staging when prenatal diagnosis was made 3:

• Higher antenatal stages (3-4) independently predict both perinatal mortality and severe neonatal morbidity 3
• Stage 4 TAPS (with donor hydrops) carries an odds ratio of 7.9 for severe neonatal morbidity 3
• Earlier gestational age at birth significantly increases both mortality and morbidity risk 3