Learn More
 Twin Reveresed Arterial Perfusion (TRAP) Sequence
Minimize

What is Twin Reveresed Arterial Perfusion (TRAP) sequence?

Twin Reversed Arterial Perfusion (TRAP) sequence is a rare (1 in 35,000 pregnancies or 1% of monozygotic twin pregnancies) condition in which there is one normal appearing baby and another with multiple lethal anomalies. This situation results when artery-to-artery anastomoses on a shared placenta cause the perfusion pressure of one twin to overtake that of the other, which then has reveresed arterial flow.  Blood from the pump or normal twin enters the recipient's iliac vessels so that the lower part of the body is perfused more than the upper part.  This results in the acardius fetal malformation, or acardiac twin.

The  acardiac twin can present in various ways, but the most common is in which the fetus develops with neither a heart (hence, acardiac) or a head, which is incompatible with life.  The pump twin is typically structurally normal, however the added circualatory burden can lead to cardiomegaly (enlarged heart) and heart failure that may progress to hydrops fetalis.  This results in a mortality rate of 50-75% for the pump twin.

The risk of chromosomal anomalies in pregnancies with TRAP sequence has been reported in  up to 50% of the pump twins.  It has been suggested that the abnormal karyotype, although not responsible for the TRAP sequence, may increase the likelihood of discordant development. 

How is it diagnosed?

Acardiac twinning is usually recognized by early ultrasonographic examination.  One twin (pump) appears structurally normal while the other (acardiac/TRAP twin)  typically has no heart and often no upper body structures.  Color doppler demonstrates arterial blood flow perfusing the acardiac/TRAP twin in a retrograde fashion.

What treatment is available?

Most often, we utilize RadioFrequency Ablation to interrupt the blood supply of the acardiac twin.  This is a procedure typcially done in the Maternal Fetal Medicine office, under ultrasound guidance with local anesthesia(Lidocaine).  The procedure itself is fairly quick, taking approximately 15 minutes.  Patients are allowed to eat/drink normally prior to the procedure, and are able to return home usually about 30 minutes post-procedure.  We recommend having someone with you during the procedure for support, and to drive you home and then recommend "couch-potato" rest for 24-48 hours.

When is treatment recommended?

Treatment is recommeded between 16 and 26 weeks of pregnancy for cases in which the TRAP sequence demonstrates significant stress on the health of the pump twin or the pregnancy in general.  Indicators for poor prognosis in which treatment is indicated include:

  • Acardiac twin is > 50% the size of the pump twin
  • Pump twin with polyhydramnios or hydrops
  • Resistence index between pump and acardiac twin of <0.2

 

What is Twin Reveresed Arterial Perfusion (TRAP) sequence?

Twin Reversed Arterial Perfusion (TRAP) sequence is a rare (1 in 35,000 pregnancies or 1% of monozygotic twin pregnancies) condition in which there is one normal appearing baby and another with multiple lethal anomalies. This situation results when artery-to-artery anastomoses on a shared placenta cause the perfusion pressure of one twin to overtake that of the other, which then has reveresed arterial flow.  Blood from the pump or normal twin enters the recipient's iliac vessels so that the lower part of the body is perfused more than the upper part.  This results in the acardius fetal malformation, or acardiac twin.

The  acardiac twin can present in various ways, but the most common is in which the fetus develops with neither a heart (hence, acardiac) or a head, which is incompatible with life.  The pump twin is typically structurally normal, however the added circualatory burden can lead to cardiomegaly (enlarged heart) and heart failure that may progress to hydrops fetalis.  This results in a mortality rate of 50-75% for the pump twin.

The risk of chromosomal anomalies in pregnancies with TRAP sequence has been reported in  up to 50% of the pump twins.  It has been suggested that the abnormal karyotype, although not responsible for the TRAP sequence, may increase the likelihood of discordant development. 

How is it diagnosed?

Acardiac twinning is usually recognized by early ultrasonographic examination.  One twin (pump) appears structurally normal while the other (acardiac/TRAP twin)  typically has no heart and often no upper body structures.  Color doppler demonstrates arterial blood flow perfusing the acardiac/TRAP twin in a retrograde fashion.

What treatment is available?

Most often, we utilize RadioFrequency Ablation to interrupt the blood supply of the acardiac twin.  This is a procedure typcially done in the Maternal Fetal Medicine office, under ultrasound guidance with local anesthesia(Lidocaine).  The procedure itself is fairly quick, taking approximately 15 minutes.  Patients are allowed to eat/drink normally prior to the procedure, and are able to return home usually about 30 minutes post-procedure.  We recommend having someone with you during the procedure for support, and to drive you home and then recommend "couch-potato" rest for 24-48 hours.

When is treatment recommended?

Treatment is recommeded between 16 and 26 weeks of pregnancy for cases in which the TRAP sequence demonstrates significant stress on the health of the pump twin or the pregnancy in general.  Indicators for poor prognosis in which treatment is indicated include:

  • Acardiac twin is > 50% the size of the pump twin
  • Pump twin with polyhydramnios or hydrops
  • Resistence index between pump and acardiac twin of <0.2

 

Twin to Twin Transfusion Syndrome | TRAP Sequence | Selective Intrauterine Growth Restriction (SIUGR)
Copyright 2009 by Evergreen Fetal Therapy
Terms Of Use | Privacy Statement