Conjoined twins are twins whose bodies are joined together at birth. This happens where the zygote of identical twins fails to completely separate. Conjoined twins occur in an estimated one in 200,000 births, with approximately half being stillborn. The overall survival rate for conjoined twins is between 5% and 25%. Conjoined twins are more likely to be female (70-75%). There are several different types of conjoined twin: Thoracopagus: bodies fused in the thorax. The heart is always involved in these cases; when the heart is shared, prospects for a long life, either with or without separation surgery, are poor. (35-40% of cases) Omphalopagus: joined at the lower chest. The heart is not involved in these cases but the twins often share a liver, digestive system, diaphragm and other organs. (34% of cases) Xiphopagous: bodies fused in the xiphoid cartilage, e.g., Chang and Eng Pygopagus (iliopagus): joined, usually back to back, to the buttocks (19% of conjoined twins) Cephalopagus: heads fused, bodies separated. These twins cannot survive due to severe malformations of the brain. Also known as janiceps (after the two-faced god Janus) or syncephalus. Cephalothoracopagus: bodies fused in the head and thorax. These twins cannot survive. (also known as epholothoracopagus or craniothoracopagus) Craniopagus: skulls fused, but bodies separate (2%) Craniopagus parasiticus - a second bodyless head attached to the head Dicephalus: two heads, one body with two legs and two, three, or four arms (dibrachius, tribrachius or tetrabrachius, respectively. Abigail and Brittany Hensel, 15-year-old conjoined twins from the United States, are of the dicephalus tribrachius type. Ischiopagus: Anterior union of the lower half of the body, with spines conjoined at a 180° angle. (6% of cases) Ischio-omphalopagus: Twins are conjoined with spines in a Y-shape. They have four arms and usually two or three legs. These cases can be challenging because the twins often share reproductive and excretory systems. Parapagus: Lateral union of the lower half extending variable distances upward, with the heart sometimes involved. (5% of cases) Diprosopus: One head, with two faces side by side. In some cases, parts of the brain have been known to be shared between conjoined twins joined at the head. Occasionally one of the twins will fail to develop properly, effectively acting as a parasite upon the normally developed twin: this condition is known as parasitic twinning or asymmetic conjoined twins. One twin may absorb the other, which is known as inclusion twinning. Natural death of the twins can occur within hours or a few days. Original text: http://en.wikipedia.org/wiki/Conjoined_twins SEPARATION OF CONJOINED TWINS Some pairs, depending on the degree of conjunction—in particular, the degree to which they share internal organs—can be separated by surgery. In July 2003 two women from Iran, Ladan and Laleh Bijani, who were joined at the head but had separate brains (craniopagus) were surgically separated in Singapore, despite surgeons' warnings that the operation could be fatal to one or both. Both women died during surgery. One ethical issue with separation is when the operation will result in the death of one twin (for example, in the case where they are sharing a heart.) A notable case was that of the Attard sisters (Gracie and Rosie), the daughters of Rina and Michaelangelo Attard of the Maltese island of Gozo. The twins were known to the world media as "Mary" and "Jodie" to protect the privacy of the family during their ordeal. Despite the opposition of the Attards, the High Court of Justice of England and Wales ruled that the twins should be separated, even though this would (and did in 2001) cause the death of Rosie ("Mary"), the weaker twin. Most recently, an attempt was made to separate the German conjoined twins Lea and Tabea Block. Tabea died September 16, 2004 just minutes after having been separated from her twin sister. Original text: http://en.wikipedia.org/wiki/Conjoined_twins