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TRAP Sequence — Fetoscopic Cord Occlusion Treatment

Twin reversed arterial perfusion sequence in monochorionic twin pregnancy where an acardiac twin is perfused by reversed arterial flow from a structurally normal pump twin, treated with fetoscopic cord occlusion or radiofrequency ablation to protect pump twin survival.

Written by: Saygı Hospital Health Guide Editorial Board
Published:

This content is for general information; please consult your physician for diagnosis and treatment.

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What is TRAP Sequence — Fetoscopic Cord Occlusion Treatment?

TRAP (twin reversed arterial perfusion) sequence is a rare condition in monochorionic monozygotic twin pregnancies (incidence 1 in 35,000) where one twin develops without a functional heart (acardiac twin) and is perfused by retrograde arterial flow from the structurally normal twin (pump twin) through artery-to-artery placental anastomoses.

The acardiac twin is non-viable but acts as a parasitic mass increasing demand on the pump twin's cardiovascular system, leading to high-output cardiac failure, polyhydramnios, preterm labor, and pump twin demise in 50–75% of untreated cases.

Treatment options include fetoscopic laser cord occlusion (preferred at 16–22 weeks), bipolar cord coagulation, and radiofrequency ablation (RFA) of the umbilical cord or intra-fetal vessels of the acardiac twin; selective interruption of perfusion saves the pump twin in 80–90% of treated cases.

Symptoms

Asymptomatic in early pregnancy; detected on first or second-trimester ultrasound
Acardiac twin appears as amorphous mass without identifiable cardiac structures, often with cystic hygroma, edema, and partial body development
Reverse pulsatile blood flow from pump twin to acardiac twin demonstrated on Doppler
Pump twin signs of cardiac failure: cardiomegaly, pericardial effusion, hydrops fetalis
Polyhydramnios from acardiac mass or pump twin output state
Maternal symptoms: rapid uterine growth, dyspnea from polyhydramnios, threatened preterm labor

Risk Factors

Monochorionic twin pregnancy (monozygotic twins sharing placenta)
Triplet pregnancy with monochorionic component carries even higher TRAP risk
Assisted reproductive technology slightly increases monozygotic twinning
No specific maternal risk factors; condition arises from random placental vascular configuration
Earlier diagnosis and pump twin cardiac compromise indicate worse prognosis without treatment
Acardiac twin to pump twin weight ratio over 50% predicts pump twin failure

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Suspected TRAP sequence on routine ultrasound — urgent referral to fetal medicine center
  • Confirmed TRAP with progressive pump twin cardiomegaly, hydrops, or polyhydramnios — same-week evaluation for intervention
  • Maternal preterm labor or severe abdominal distention from polyhydramnios — emergency obstetric care
  • Decision-making about intervention timing — multidisciplinary counseling with fetal surgery team and parents
  • Postoperative bleeding, leakage, or contractions after fetoscopic procedure — immediate maternal-fetal medicine evaluation

Treatment Methods

01
Fetoscopic laser cord occlusion at 16–24 weeks — laser fiber directed via fetoscope to ablate umbilical vessels of acardiac twin; pump twin survival 70–90%
02
Bipolar cord coagulation — alternative to laser, applies bipolar energy to cord; effective with similar outcomes
03
Radiofrequency ablation (RFA) of intra-fetal pelvic vessels or cord — percutaneous needle approach under ultrasound guidance, less invasive than fetoscopy
04
Conservative management — only for very early diagnosis with small acardiac twin and stable pump twin under close monitoring; intervention recommended if cardiac compromise develops
05
Postoperative monitoring weekly with ultrasound and Doppler; tocolytic therapy and steroids for fetal lung maturity if preterm delivery threatens; delivery typically vaginal at 34–37 weeks if pump twin healthy

Which Department to Visit?

You can visit our Kadın Hastalıkları ve Doğum department for these complaints. Our specialist physicians will create the most suitable treatment plan for you.

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.