ABSTRACT
Genetically identical individuals joined by a part of their anatomy and often sharing one or more organs are known as conjoined twins. Conjoined twinning is due to incomplete division of a primitive embryonal disk destined to produce identical twins. There are supporters of a fission theory, claiming that conjoined twins are the result of an incomplete split of the embryonic axis. The location, extent and nature of the bridge between both twins vary widely, and this complicates description of the anatomy of each set. Several classifications attempt at simplifying description. Nowadays, most conjoined twins are prenatally diagnosed by ultrasound (US) in advanced countries, preventing serious obstetric problems. Except in thoracopagus with common heart and in asymmetric twins, both fetal heart tones can be identified like in regular twins. A comprehensive understanding of the anatomy of the organs and the distribution of their functions is necessary for planning viable separation strategies.
