Early versus late intervention for twin reversed arterial perfusion sequence: an open-label randomized controlled trial
*TRAPIST*: TRAP Intervention STudy

Twin reversed arterial perfusion sequence (TRAP) is a rare anomaly unique to
monochorionic twin pregnancies, with an estimated prevalence of 1 in 35 000
pregnancies but with a mortality of more than 50% for the healthy pump twin1.
Monochorionic twins are identical and share a single placenta with vascular
anastomoses that connect the two fetal circulations. TRAP is a complication of
this shared circulation and occurs if one of the twins dies in early pregnancy.
In TRAP, blood flows from a structurally normal pump twin in a reverse
direction towards its demised co-twin, which becomes a true parasite without
cardiac activity from its own, hence also called the acardiac twin. TRAP is
nowadays diagnosed already at the 12 weeks ultrasound scan and is characterized
by a monochorionic twin pregnancy with one structurally normal and one grossly
abnormal twin

If the pump twin survives to 16 weeks and is treated thereafter, approximately
80% will survive8. However, a major disadvantage of delaying the intervention
until after 16 weeks* gestation is the high mortality of the pump twin (up to
33%) between the diagnosis at 12 weeks and the planned intervention at 16
weeks9. These early demises are entirely unpredictable9. As such, the survival
rate for TRAP diagnosed at 12 weeks and treated after 16 weeks is estimated to
only about 50%8 9. Also, a recent meta-analysis demonstrated an inverse
relationship between gestational age at treatment and gestational age at birth,
suggesting that an earlier intervention may decrease the risk of very preterm
birth. An intervention at 12-14 weeks may thus prevent the early deaths and
reduce the risk of very preterm birth, but might also increase the risk the
miscarriage because of premature rupture of the membranes.

To assess if early intervention (12.0-14.0 weeks) (study group) improves the
outcome of TRAP sequence as compared to late intervention (16-18 weeks)
(control group).

International multicentre open label randomized controled trial

Early group; Intrafetal coagulation to stop reversed flow.
Late group; either Intrafetal coagulation or fetoscopic laser coagulation of
the cord and / or anastomoses. to stop reverse flow.

Burden is not higher/more as compared to standard of care. Only difference
might be earlier intervention due to randomisation outcome.