Poster abstracts of the mass. Pathological examination showed macerated tissue enclosed in an amniotic bag. The peduncle consisted of a vascular pedicle lined with amnion and could be assumed to be a umbilical cord. The mass was covered by skin and included adipose tissue and a row of cartilaginous nodules evoking the spine. Based on these findings, parasitic sacral conjoined twin was diagnosed. The infant underwent surgical removal of the precoccygeal cyst that had been confirmed on postnatal ultrasound scan. On pathological examination it corresponded to an intestinal sac that was then interpreted as part of the parasitic twin.Supporting information can be found in the online version of this abstract. Objectives: Conjoined twins are classified as symmetrical and asymmetrical (heteropagus). In the heteropagus cases, the dependent portion (parasite) is smaller than the host (autosite). It is believed that heteropagus twins result from atrophic ischemia of monozygotic conjoined twin at an early gestational age. The nomenclature is made regarding to the insertion site of the parasite. Methods: We present a case of epigastric heteropagus which is a rare occurance. Results: 31 years old primigravid patient was scanned at 23 rd weeks of gestational age and symetrical intrauterin growth restriction, anhydramniosis, omphalocele containing small intestine were found. Additional osseous structures arising from the trunk were seen. Fetal echocardiogram showed complet atrioventriculoseptal defect, ventricular asymetria and double outlet left ventricule. Amniocentesis resulted a normal 46,XY karyotype. The most striking abnormality at postmortem pathological examination was the presence of a parasitic twin inserted just above the abdominal wall defect of the host. The parasitic twin consisted of a pelvis and a pair of well-formed extremities. Conclusions: A review of reported cases of parasitic omphalopagus shows a strong male predominance and a high frequency of congenital abnormalities. Congenital heart disease has been described in about half of the cases. Complexity of the defect is variable and the quantity of functioning organ(s) in the autosite and parasite is quite variable. Prenatal ultrasound examination plays a major role in the diagnosis and the correct defition of the abnormalities helps in patient counseling with respect to prognosis for a epigastric heteropagus conjoined twin pregnancy. P23.09 P23.10Second trimester diagnosis of dicephalic thoracoomphalopagus conjoined twins via transabdominal 3D sonography N. Kim, G. Lee Department of Obstetrics and Gynecology, St. Vincent Hospital, Suwonsi, Republic of KoreaConjoined twins are very rare and the mortality of the fetus is extremely high especially with early pregnancy. The early prenatal diagnosis is very important to give the mother the chance of maling their decision whether to continue or terminate the pregnancy. Case: A 27-years old, nulliparous woman was referred to our clinic at the 14+2 gestational week because of fetal anmaly. There was no history of ...