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Twin Reversed Arterial Perfusion (TRAP) Sequence: Proposal for Morphologic Classification System Predicting Natural
1Department of Ultrasound Diagnosis, Maternal and Child Health Hospital of Hubei Province, Wuhan, China.
Prenatal Diagnosis
|March 22, 2026
Summary
A new classification for Twin Reversed Arterial Perfusion (TRAP) sequence based on skeletal morphology shows prognosis varies by acardiac twin development. Minimal structural development in the acardiac twin correlates with higher pump twin survival rates.
Area of Science:
- Perinatology
- Fetal Medicine
- Reproductive Biology
Background:
- Twin Reversed Arterial Perfusion (TRAP) sequence is a rare complication of monochorionic twin pregnancies.
- Accurate prognostication is crucial for managing TRAP sequence, especially in expectantly managed cases.
Purpose of the Study:
- To introduce a novel classification system for TRAP sequence based on skeletal morphology.
- To assess the prognostic significance of this new classification in expectantly managed TRAP cases.
Main Methods:
- Retrospective cohort study of 116 expectantly managed TRAP sequence cases (2001-2022).
- Classification into five morphological types: Type I (Hemiacardius), Type II (Acardius Holosomus), Type III (Acephalus Trunk), Type IV (Acephalus Acormus), and Type V (Acardius Amorphous).
- Comparison of pump twin outcomes across the five morphological types.
Main Results:
- Type III (Acephalus Trunk) was the most prevalent (41.4%).
- Overall adverse outcome rate was 75.0% (87/116).
- Significant differences in pump twin survival rates were observed across types (p=0.001), with Type V (Acardius Amorphous) showing the highest survival (66.7%) and Type I (Hemiacardius) the lowest (15.0%).
Conclusions:
- Pump twin survival in expectantly managed TRAP sequence is associated with the degree of acardiac twin structural development.
- The proposed skeletal morphological classification system may aid in early sonographic assessment and prenatal counseling for TRAP sequence.
