Twin-Reversed Arterial Perfusion Sequence / TRAP Sequence
Fetal Surgery for Twin-Reversed Arterial Perfusion / TRAP Sequence
TRAP Sequence References | Contact Us / Request an Appointment
Twin-reversed arterial perfusion / TRAP sequence occurs only in the setting of a monochorionic gestation and complicates approximately 1% of monochorionic twin gestations, with an incidence of 1 in 35,000 births.
In the TRAP sequence the acardiac / acephalic twin receives all of its blood supply from the normal "pump" twin.
The term reversed perfusion is used to describe this scenario because blood enters the acardiac / acephalic twin retrograde through its umbilical artery and exits through the umbilical vein.
Because of increased demand the abnormal circulation in TRAP sequence places on the heart of the pump twin, cardiac failure is the primary concern in TRAP sequence. If left untreated, the pump twin dies in 50% to 75% of cases. This is especially true when the acardiac / acephalic twin weighs more than 50% of the estimated weight of the pump twin.
It is important to exclude a chromosomal abnormality before offering a fetoscopic procedure in TRAP sequence, because the incidence of chromosomal abnormality in the pump twin may be as high as 9%. Fifty-one percent of TRAP sequence pregnancies are complicated by polyhydramnios, and 75% are complicated by preterm labor.
The difference in estimated fetal weight between the pump twin and the acardiac / acephalic twin is predictive of outcome. When the acardius–to–pump twin weight ratio exceeds 0.5, adverse pregnancy outcome is predicted in 64% of cases.263 If this weight ratio is greater than 0.7, the adverse pregnancy outcome for the pump twin is approximately 90%.
Techniques of sectio parva (selective removal of an anomalous twin) and ultrasound-guided embolization were used in an attempt to interrupt the vascular communication between the pump twin and the acardius. These procedures have been associated with substantial morbidity and unreliable outcomes, which led to the development of fetoscopic approaches to this problem.
McCurdy and associates were the first to report a case of fetoscopic cord ligation in TRAP sequence. The acardiac / acephalic twin's cord was successfully ligated, but only after the pump twin's cord was ligated and then released after the error was recognized. The pump twin developed persistent bradycardia and was noted to be dead on ultrasound examination on postoperative day one.
Quintero et al, reported the first successful umbilical cord ligation for TRAP sequence. The procedure was performed at 19 weeks of gestation, using two percutaneous trocars and a 1.9-mm endoscope. The cord was successfully ligated, and except for some mild postoperative uterine irritability, the patient responded well.
Three weeks following the procedure the mother presented with leakage of amniotic fluid that subsequently resolved. The pregnancy continued until 36 weeks of gestation, when a healthy boy was delivered.
Twin-Reversed Arterial Perfusion / TRAP Sequence Treatment Techniques
A number of different techniques have been used to treat TRAP sequence including 40 cases of cord occlusion by emolization in 5, ligation in 15, laser photocoagulation in 10, bipolar diathermy in 7, monopolar diathermy in 3. Intrafetal ablation has also been performed by alcohol injection in 5, monopolar diathermy in 3, interstial laser in 4, and radiofrequency ablation in 13.
In a review of the various techniques that have been reported to treat TRAP sequence, Tan et al concluded that intrafetal radiofrequency ablation was associated with lower rate of premature delivery, rupture of membranes before 32 weeks' gestation (23 vs verses 58% for other techniques), and a higher rate of clinical success than cord occlusion techniques.
Return to Top
Healey MG: Acardia: Predictive risk factors for the co-twins survival.Teratology 50:205, 1994.
James WH: A note on the epidemiology of acardiac monsters.Teratology 16:211, 1977.
McCurdy CM, et al: Ligation of the umbilical cord of an acardiac-acephalus twin with an endoscopic intrauterine technique.Obstetric Gynecology 82:708, 1993.
Michejda M: Intrauterine treatment of spina bifida.Primate model. Z Kinderchir 39:259, 1984.
Moore TR, et al: Perinatal outcome of forty-nine pregnancies complicated by acardiac twinning.American Journal of Obstetrics and Gynecology 163:907, 1990.
Porreco RP, et al: Occlusion of umbilical artery in acardiac-acephalic twin. Lancet 337:326, 1991.
Robie GF, et al: Selective delivery of an acardiac-acephalic twin.New England Journal of Medicine 320:512, 1989.
Tan TY, Sepulveda W: Acardiac twin: a systematic review of minimally invasive treatment modalities.Ultrasound Obstet Gynecol 4: 409-419, 2003.
Tsao KJ, Feldstein VA, Albanese CT, et al: Selective reduction of acardiac twin by radiofrequency ablation.American Journal of Obstetrics and Gynecology 187:635-640, 2002.
Van Allen MI, et al: Twin reversed arterial perfusion (TRAP) sequence: A study of 14 twin pregnancies with acardius.Semin Perinatol 7:285, 1983.
Return to Top
To request an appointment at the Fetal Care Center of Cincinnati or contact us, please use our secure, online appointment form or call 1-888-338-2559 (1-888-FETAL59).
Return to Top
Revised 3/05
