The sonographic appearance of acardiac twin may differ in many cases, but a hydropic fetus without cardiac activity is the main manifestation of TRAP sequence. Reversed arterial flow in the umbilical artery from pump twin to acardiac twin is revealed in spectral Doppler examination [6]. Furthermore, most acardiac twin presents umbilical artery malformations, and according to Roberto Ruiz-Cordero, 78% of acardiac twin shows single umbilical artery and in 22% of cases, three vessel umbilical cord with thrombosis is described [7]. In majority of cases, pump twin develops high cardiac output failure including cardiomegaly, pericardial effusion and tricuspid regurgitation with polyhydramnios. Therefore, echocardiography is mandatory for the assessment and surveillance of cardiac function in pump twin [8]. The perinatal mortality of pump twin has been reported to range from 35 to 55% [9]. In our case, the pump twin demonstrated normal structural development. However, some degrees of cardiomegaly and mild tricuspid regurgitation in echocardiography and polyhydramnios were found, all of which were considered as a looming threat of fetal demise. All the abovementioned criteria associated with excessive volume of the acardiac twin predicted poor pregnancy outcome.
Intrauterine fetal demise and intra-amniotic or placental tumours such as placental teratoma should be considered as the differential diagnosis for TRAP sequence. However, precise evaluation of spinal development and umbilical cord attachment can be beneficial for differentiation [8].
There is a variety of treatment modalities which can improve perinatal survival. In minimally invasive techniques, vascular anastomosis is interrupted by alcohol, diathermy, cord embolization or coagulation, laser therapy or radiofrequency ablation [10]. Eventually, the most crucial component in treatment is likely to detect this complication early in pregnancy and perform appropriate interventions before detrimental consequences occur.