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%).

The term Siamese Twins comes from what are probably the most famous pair, Chang and Eng Bunker (1811-1874), Chinese Americans born in Siam, now Thailand. The term is frequently used as a synonym for conjoined twins. The earliest known case of conjoined twins dates from the 1100s, the British sisters Mary and Eliza Chulkhurst.

There are several different types of conjoined twin:

• Thoracopagus: bodies fused in the thorax (35-40% of cases)
• Omphalopagus: joined at the lower chest (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
  • Cephalothoracopagus: bodies fused in the head and thorax (also known as epholothoracopagus or craniothoracopagus)
• Craniopagus: skulls fused (2%)
  • Craniopagus parasiticus - a second bodyless head attached to the head
• Dicephalus: two heads, one body with two legs and two arms. Only four recorded cases who survived. Best known of those are Abigail (Abby) and Brittany (Britty) Hensel. In that sort of twin, nearly always the left component's heart is defective.
• Ischopagus: Anterior union of the lower half of the body, not involving the heart (6% of cases)
• 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.

Natural death of the twins can occur within hours or a few days.

Separating 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 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 on July 8, 2003.

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. Despite the opposition of the Attards, the High Court of Justice of England and Wales ruled that their twins should be separated, even though this would, and did in 2001, cause the death of Rosie, 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.

See also

• List of twins

External links

Wikimedia Commons has multimedia related to Conjoined twins .

• Types of conjoined twins http://zygote.swarthmore.edu/cleave4a.html
• A social history of conjoined twins http://zygote.swarthmore.edu/cleave4b.html
• Case studies of conjoined twins http://www.modcult.brown.edu/students/angell/twinsoperation.html
• Photos and ancient drawings & extensive examples http://phreeque.tripod.com/conjoined_twins.html
• Article on the ethical issues surrounding separating conjoined twins http://www.bumc.bu.edu/www/sph/lw/pvl/lim/conjoined-01-apr5.htm