USF Fetal Therapy Center
USF Health - College of Medicine

Acardiac Twin or Twin Reversed-Arterial Perfusion (TRAP) Sequence:
Information for Healthcare Professionals

Twin reversed-arterial perfusion (TRAP) sequence is a rare and serious complication of monozygotic multiple gestations, affecting 1% of monozygotic twins or 1 in 35,000 births. Although the pathophysiologic mechanism responsible for the syndrome is not completely understood, it has been hypothesized that blood is perfused by the hemodynamically advantaged twin ("pump" twin) to the other twin ("acardiac" twin) by means of retrograde flow via an arterio-arterial and a veno-venous anastomosis in a monochorionic placenta. Thus, the acardiac twin receives deoxygenated arterial blood from the pump twin. Although the pump twin is structurally normal, expectant management is associated with a perinatal mortality rate of 50-75%, largely as a result of high-output heart failure or premature delivery caused by polyhydramnios and/or rapid growth of the acardiac twin.

Fetoscopy

Diagnosis

This inadequate perfusion of the acardiac twin is responsible for a spectrum of characteristic and invariably lethal set of anomalies, including acardia, acephalus, severe maldevelopment of the upper body, variable limb and organ reductions, malformations, and a relative excess of edematous connective tissue, which are detected with ultrasound.

Risk factors associated with an increased likelihood of pregnancy loss include:

  • Polyhydramnios
  • Large TRAP twin (estimated fetal weight of the acardiac twin is 50% or greater than that of the pump twin)
  • Hemodynamic decompensation of the pump twin, as evidenced by hydrops or abnormal Doppler waveform changes
  • Monoamniotic TRAP
  • Preterm labor
  • Shortened cervix (<2.5 cm)

Treatment

Patients with TRAP sequence with risk factors (as described above) managed via umbilical cord occlusion, treated at our center, show a more favorable outcome compared to surgical candidates that do not undergo fetal surgery. Our center offers the most advanced techniques of umbilical cord occlusion for the management of TRAP sequence. Please see our webpage Umbilical Cord Occlusion of Discordant Anomolous Twins(link) for a description of in utero treatment techniques.

Referrals

Please contact us to fax the Acardiac Twin Evaluation/Screening Form and fax it to 813-259-0839. For further information, please feel free to contact us.

Phone Toll Free: 1-877-FETAL-77
Phone: 813-259-8513
Fax: 813-259-0839
Email: sdzabel@tgh.org 

References

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