What is the TRAP sequence?
TRAP sequence (twin reversed arterial perfusion) is one of the complications of monochorial twin pregnancy (which means that the twin children share only one placenta), in which one twin has an acardius (no heart) and also very often an acranius (no head).
The affected twin, which is not viable in any case, is supplied by the healthy one via arterio-venous anastomoses (hence the name TRAP sequence). Anastomoses are connections between blood vessels, in this case between the two twins.
The TRAP sequence is a rarity in obstetrics, occurring in only 1 in 35,000 births.
How is the diagnosis made?
The diagnosis is made in early pregnancy by ultrasound.
What is the prognosis for the healthy child?
Because the heart of the healthy fetus has two bodies to supply, this often results in heart failure of the pumping twin, polyhydramnios, premature birth, and a mortality rate of up to 41%.
How is the TRAP sequence treated?
There are several methods to separate the Acardius-Acranius twin from the circulation of the healthy fetus. Common is laser coagulation of the placental anastomosis or umbilical cord. For this, ultra-thin device technology with 1mm optics is used to reduce the risks of fetoscopic surgery.
How is the laser surgery performed?
Laser surgery is usually performed under local anesthesia of the abdominal wall. The ultra-thin 1mm optics reduces the risk of premature rupture of membranes after the performed fetoscopy. At the end of the operation, Doppler ultrasound is used to carefully check whether the vascular supply to the acranius-acardius is completely interrupted.
Overall, only very few operations have been performed for this clinical picture, as the condition is extremely rare.