Siamese twins--prenatal diagnosis in the first trimester of pregnancy. Case study and review.

Conjoined twins are a unique type of monozygotic twins. All monozygotic twins should be thoroughly evaluated for incomplete separation and, if incomplete separation is diagnosed, the extent of internal organ connection and the presence of additional developmental anomalies of the foetuses should be assessed. Common heart of foetuses is particularly difficult to diagnose and crucial for prognosis. We present an example of female thoracoomohalopagus twins with a common triventricular heart, connate livers, and joined hepatic vessels, diagnosed in week 12 of pregnancy Due to the high complexity of foetal connection, separation was not possible and following interdisciplinary consultation, the pregnancy was aborted upon the patient's request in week 16.