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Acardiac twin or twin reversed arterial perfusion (TRAP) sequence is a rare medical complication of Monozygotic twins. Taiwanese Obstetricians usually treat TRAP sequence conservatively. Occasionally, repeated amnio-reduction is performed to decompress the polyhydramnios caused by the TRAP sequence, even though there was no correction of the pathophysiologic mechanism. Radiofrequency ablation is a minimally invasive, percutaneous technique that can effectively obliterate blood supply to an acardiac twin to preserve and protect the pump twin. This recent technique has never been used before for the treatment of the TRAP sequence in Taiwan. This article reported the first-hand experience of acardiac twin management with RFA in Taipei Chang Gung Memorial Hospital.

This paper suggests that during the time of the "splitting process" that produces monozygotic twins the number of cells may not be evenly distributed to the future twins. The outcome of this 'irregular division' may be the twin-to-twin transfusion syndrome and acardiac twins.

Resume Au premier trimestre, l’echographie de 12 semaines est capitale pour depister les anomalies chromosomiques par la clarte nucale, pour reconnaitre precocement des malformations graves, pour etablir le type du placenta (monochorial ou bichorial). La chorionicite determine les strategies de depistage et de diagnostic prenatal ainsi que de prise en charge obstetricale. Au deuxieme trimestre le depistage chromosomique par les marqueurs seriques est moins efficace et le diagnostic echographique des malformations est plus difficile que dans les grossesses monofœtales. Quand une anomalie grave existe chez un seul fœtus, il est possible d’interrompre selectivement la grossesse. Cette intervention, tres aleatoire quand le placenta est monochorial, est bien codifiee quand il est bichorial. Son risque est plus faible au premier trimestre, ce qui souligne l’interet d’un diagnostic prenatal precoce chez les jumeaux. Un placenta de type monochorial expose a des complications specifiques, comme le syndrome transfuseur-transfuse. Celui-ci peut etre traite par photocoagulation au laser dans les formes graves et precoces, ou par amniodrainage dans les formes les plus moderees.

Acardiac twinning is caused by twin reversed arterial perfusion (TRAP). Normal “pump” twins may face early delivery and cardiac decompensation and have a high perinatal mortality. A primagravid patient had serial evaluation of a TRAP pregnancy beginning early in the second trimester. Rapid growth of the acardiac sibling, high diastolic velocity Doppler waveforms in the perfusing vessel, and early hydramnios prompted ablation of blood flow by a percutaneous ultrasonographically guided infusion of absolute alcohol. A term birth of a normal pump twin was the outcome. Ablation of blood flow into an acardiac sibling of a TRAP pregnancy may be indicated in cases with a poor prognosis by use of an effective percutaneous ultrasonographically guided technique.

Understanding the significant increased risks associated with twin pregnancies requires knowledge of the embryogenesis of twins and the unique placental characteristics seen only in twin gestations. Dizygotic "fraternal" twins, 70% of all twins, are at relatively low risk when compared with monozygotic twins, largely due to abnormalities seen in association with monochorionic placentation. The sonographic determination of chorionicity and amnionicity allows better estimation of pregnancy risk--up to 50% mortality in monochorionic-monoamniotic twins. Careful evaluation of intrauterine twin growth assists in the early identification of fetal abnormalities because normal twin growth should parallel that of singleton pregnancies until late in the third trimester. A number of the unique complications affecting growth in twin pregnancies are discussed, including twin transfusion syndrome, the "stuck twin" phenomenon, twin embolization syndrome, and development of acardiac twins.

S RADIOFREQUENCY ABLATION FOR TWIN-REVERSED ARTERIAL PERFUSION E: THE NORTH AMERICAN FETAL TREATMENT NETWORK (NAFTNET) EXPERIENCE HANMIN LEE, TIMOTHY CROMBLEHOLME, DOUGLAS WILSON, University of California, San Francisco, San Francisco, California, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania OBJECTIVE: Significant mortality occurs with Twin-Reversed Arterial Perfusion (TRAP) sequence due to a high output state in the normal or “pump” twin as well as return of doubly-deoxygenated blood. Multiple strategies have been used to stop flow in the acardiac mass to prevent complications. Radiofrequency ablation is a minimally invasive method for treatment of TRAP sequence. We report a case series of 83 patients undergoing radiofrequency ablation of the acardiac mass for the treatment of TRAP sequence. STUDY DESIGN: A multi-institutional restrospective review was performed of all cases from ten member institutions of the North American Fetal Treatment Network. Maternal variables included surgical complications and length of hospital stay. Prenatal variables included size of the acardiac fetus, IUFD, and amnionicity. Postnatal outcome variables included gestational age at delivery and survival to one month of age. RESULTS: There were two instances of postoperative failure with persistence of flow to the acardiac twin. Length of stay after the RFA was 1.19 / 0.76 days. The mean size of the acardiac mass was 103 / 73% that of the normal twin. There were 9 pump twin IUFD’s. Overall newborn survival to one month for pump twins was 81% overall (67/83). Survival in monochorionic/diamniotic twin pregnancies was 85% (58/68) with an average gestational age at delivery of 34.5 weeks; for monochorionic/monoamniotic twin pregnancies was 33% (2/6) with an average gestational age of delivery at 26.7 weeks; and for triplet pregnancies with a monochoronic, diamniotic pair, 78% (7/9) with an average age at delivery of 31.3 weeks. CONCLUSION: This is the largest reported series of patients treated with TRAP sequence. RFA of the acardiac mass is an effective, minimally invasive treatment for TRAP sequence with improved results compared to previously published series using other techniques. Additional monochorionic/monoamniotic cases are needed to better define outcomes.