Conjoined twins

:For the Japanese composer Siamese Twin, see AQi Fzono.

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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%).

Related Topics:
Twin - Zygote - Identical twin

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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.

Related Topics:
Chang and Eng Bunker - 1811 - 1874 - Thailand - Mary and Eliza Chulkhurst

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There are several different types of conjoined twin:

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• 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 survived; the best known of these are Abigail (Abby) and Brittany (Britty) Hensel.
• 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.

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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.

Related Topics:
Parasite - Parasitic twin

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

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Conjoined twins: Separating conjoined twins ►