TRAP
The TRAP sequence is a rare complication of
monozygotic multiple gestations that affects 1%
of monozygotic twins or 1 in 35,000 births [19].
The pathophysiologic mechanism that is responsible
for the syndrome is not well known [20]; it has
been hypothesized that blood is perfused by the
hemodynamically advantaged twin (‘’pump’’ twin)
into the other twin (‘’acardiac’’ twin) by means of
retrograde blood flow through an arterioarterial and
a venovenous anastomosis in a MC placenta [20].
Thus, the acardiac twin receives deoxygenated
arterial blood from the pump twin. This inadequate
perfusion of the acardiac twin is responsible for a
spectrum of characteristic and invariably lethal set of
anomalies, which include acardia, acephalus, severe
maldevelopment of the upper body, variable limb
and organ reductions, malformations, and a relative
excess of edematous connective tissue [21].