TRAP syndrome: case report and perspectives of prenatal therapy

Lech Dudarewicz, MD, PhD; Prof. Jan Deprest, MD; LĂ©onardo Gucciardo, MD

Lech Dudarewicz, MD, PhD*; Prof. Jan Deprest, MD**; LĂ©onardo Gucciardo, MD***.

*     Polish Mother’s Memorial Hospital, Department of Genetics, 281/289 Rzgowska St. 93-338 Lodz, Poland; Ph: 48 42 271 11 83;
**    Leuven, Belgium;
***   Obstetrics and Gynecology specialist, PhD Research Fellow, Centre for Surgical Technologies, Fetal Medicine Unit Department of Obstetrics and Gynecology, University Hospitals Leuven.

Case report

A 30-year-old primipara with an uneventful family and environmental history was referred to our Department of Genetics for karyotyping at 15 weeks’gestation. The observation of an hydropic fetus in a monochorionic diamniotic twin pregnancy was the main indication.

During the pre-amniotic fluid sampling scan, absence of heartbeat in the hydropic fetus was noticed. The procedure was stopped, and the pregnancy was finally diagnosed as monochorionic monoamniotic with a twin reversed arterial perfusion (TRAP) sequence. The presentation was quite atypical with an acardiac fetus showing relatively well-developed cranial structures with underdeveloped lower part of body and lower limbs. The biometry of the donor (pump) fetus was compatible with a 15 weeks pregnancy. The acardiac fetus biometric measurements were difficult to assess because of hydrops and abnormal anatomy. Visible jugular sac, almost fully developed cranial vault, two cerebral hemispheres with ventriculomegaly, abnormal diencephalon and cerebellum, cystic structure in the chest and rudimentary limbs were observed. A reversed blood stream with present end-diastolic velocities was detected in the acardiac fetus, no fetal movements were noticed. At that time the scan of the pump twin was considered as normal. The patient was discharged home after the amniocentesis, and an ultrasound control was scheduled at 17 weeks. In the meantime, because of the absence of established fetoscopic surgical facility in Poland, we asked Pr Jan Deprest from Leuven in Belgium, for help and advice.

The proposed therapy was clamping and transsection of the acardiac cord. In the opinion of Dr Deprest the intervention should be taken into consideration at a later stage as very early fetoscopy is related with high risk of premature rupture of the membrane (PROM), particularly if the procedure is within the same sac. At the 17 weeks scan, no flow was detected in the umbilical cord nor in the body of the acardiac twin. There was only a marked twinkling Doppler artefact behind the bony structures. Additionally, the pump twin showed significantly decreased heart contractility with a suspected subvalvular VSD and pericardial effusion, inversed A wave in ductus venosus and pulsatile flow in the umbilical vein. The FHR was 135/min. The bowels were hyperechogenic, interpreted as a marker of ischemia that was associated with a observed centralisation of fetal circulation. The bladder was empty during the whole examination (45 minutes). The biometry of the pump fetus at that time was compatible with a 17+4 weeks pregnancy, and the CRL of the acardiac fetus was equivalent to 15 weeks’ gestation. Between the two ultrasound examinations the growth of the acardiac fetus was significant.

The above mentioned signs were indicators of a cardiac failure of the pump twin. Cardiovascular decompensation of the pump fetus is a possible explanation for absence of Doppler signal in a still growing acardiac fetus, the blood flow is too slow to be detected by usual color Doppler. Decompensation of the pump fetus made the decision of an urgent intervention obvious. The patient was referred to the Clinic of Obstetrics and Gynaecology of the Catholic University of Leuven in Belgium for a fetoscopic treatment.

Unfortunately at the pre-procedure scan death of the pump fetus was diagnosed.

Here are some images and videos of a second trimester acardiac twins sequence (twin reversed arterial perfusion).

Images 1 and 2: Head of the acardiac twin (transverse planes).


Images 3 and 4: Image 3 - skull of the acardiac twin; Image 4 - spine of the acardiac twin.



Images 5 and 6: Image 5 - pulsed Doppler curve at the level of the descending aorta of the pump twin. Image 6 shows reversed flow at the level of the ductus venosus of the pump twin.


Images 7 and 8: Four-chamber view of the pump heart with a small ventricular septal defect.


Videos 1, 2: Videos shows the acardiac twin.



Videos 3, 4: Videos shows the acardiac twin. At video 4 the thin umbilical cord of the acardiac twin is visible.

Videos 5, 6: Video 5 shows four-chamber view of the pump fetus heart with ventricular septal defect. Video 6 shows both acardiac and pump twin.


This case of TRAP sequence has a quite unfrequent phenotype, as the morphology of the acardiac foetus showed relatively well developed cranial structure associated with underdeveloped lower body and limbs. In typical acardiac fetus cases underdevelopment of the cephalic part is explained by the reversed direction of blood flow. A constant feature of TRAP sequence is artery-artery anastomosis leading to perfusion of deoxygenated blood from the “donor” twin to the acardiac twin. The abnormal circulation may result in early tissue hypoxia, leading to secondary atrophy of the heart and other organs. We can hypothesize that the degree of cranial structure atrophy can be related to the level of vascular connection between umbilical arteries and systemic vessels with as consequence, variations in subsequent tissue hypoxia. This supposition however cannot be proven here on the ground of the ultrasound findings.

At the admission of the patient, the amnionicity of the pregnancy was not ascertained, we believe that the pregnancy was monochorionic monoamniotic, and for us, the visualized amnion floating freely in the amniotic fluid was a sign of delayed amnio-chorionic fusion (related to hydrops in the acardiac twin) which is a frequent finding in this pathology. Anecdotally on the outside examinations the referring doctor was puzzled by the lack of heart motion with concomitant present blood flow. As a differential diagnosis the twinkling artefact, also observed in our patient, should be kept in mind, the clue being its presence behind the bones.


Further studies are needed to better understand the natural history of TRAP, to develop and validate prognosis factors. Consensual criteria are still nowadays lacking to make a selection early in gestation between patients who need a fetal intervention and the TRAP sequences that just need a close follow-up.

There is no evidence-based data whether it is best to wait until the nearly heart decompensation, or to intervene very early without signs of cardiac function failure. With such a low prevalence, building a formal study to settle this issue remains difficult. Vascular flow assessment in the acardiac fetus can be very tricky, even by power Doppler. A very weak, almost undetectable flow is quite often interpreted as absent. In this situation the acardiac fetus should be controlled 2 weeks later, a growing mass only possible with perfusion.

The difference between monoamniotic and diamniotic pregnancy is essential. The procedure-related risk of premature rupture of membranes and fetal mortality rates are different. Monochorionic diamniotic twins with an oligohydramnios of the heart decompensated fetus can be wrongly considered as a monoamniotic pregnancy.


Stevenson RE, Jones KL, Phelan MC, Jones MC, Barr M Jr, Clericuzio C, Harley RA, Benirschke K. Vascular steal: the pathogenetic mechanism producing sirenomelia and associated defects of the viscera and soft tissues. Pediatrics 1986 Sep; 78(3):451-7.


Discussion Board

Start a discussion about this article
Add bookmark Bookmarked