<aside>

Specific and severe complication of monochorionic multiple pregnancy, characterized by vascular anastomosis and partial/complete lack of cardiac development in one twin.

</aside>

https://www.youtube.com/watch?v=Jzb2vuyLrFM

TRAP sequence occurs when a normal or ‘pump’ twin perfuses an acardiac mass via placental vascular connections that are found only in monochorionic placentae. The pump twin perfuses the acardiac mass with deoxygenated blood in a retrograde manner via a placental arterioarterial anastomosis and the acardiac mass returns further deoxygenated blood back to the pump twin through a direct venovenous anastomosis.

Radiology

US features:

• Gross differences in biometrical measurements of twins
• Absence of morphologically normal heart in one twin associated with several other malformations in head, trunk, upper and lower extremities
• Subcutaneous edema and fluid collections in anomalous twin
• Color doppler (CHARACTERISTIC): Paradoxical circulation in the acardiac twin, with arterial blood flowing towards, rather than away and in a caudal-to-cranial course in the abdominal aorta, which may be evident even during the first trimester.

Color Doppler image of an acardiac twin at 14 weeks showing reverse perfusion through the umbilical cord. Vitucci, A., Fichera, A., Fratelli, N., Sartori, E., & Prefumo, F. (2020). Twin Reversed Arterial Perfusion Sequence: Current Treatment Options. International journal of women’s health, 12, 435–443. https://doi.org/10.2147/IJWH.S214254

Differentials

Differences between TTTS and TAPS. | TAPS and TOPS: Two Distinct Forms of Feto-fetal Transfusion in Monochorionic Twins – Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Diff-erences-between-TTTS-and-TAPS_tbl1_41124592 [accessed 20 Dec, 2020]

Management

<aside>

The main goals in the management of the TRAP sequence are preserving the survival of the pump twin and reaching the term for delivery.

</aside>

(2020) TRAP Sequence or Acardiac Twin | UCSF Fetal Treatment Center. Retrieved December 20, 2020, from https://fetus.ucsf.edu/trap-sequence