![]() ![]() The heart is always involved in these cases. Thoracopagus (18.5%): Two bodies fused from the upper thorax to lower belly.These twins usually share a heart, and may also share the liver or part of the digestive system. Thoraco-omphalopagus (28% of cases): Two bodies fused from the upper chest to the lower chest.The most common types of conjoined twins are: Types of conjoined twinsĬonjoined twins are typically classified by the point at which their bodies are joined. Due to the brothers' fame and the rarity of the condition, the term "Siamese twins" came to be used as a synonym for conjoined twins. In modern times, they could have been easily separated. Chang and Eng were joined by a band of flesh, cartilage, and their fused livers at the torso. Barnum's circus for many years and were labeled as the Siamese Twins. The most famous pair of conjoined twins was Chang and Eng Bunker (Thai: อิน-จัน, In-Chan) (1811 –1874), Thai brothers born in Siam, now Thailand. Conjoined twins share a single common chorion, placenta, and amniotic sac, although these characteristics are not exclusive to conjoined twins as there are some monozygotic but non-conjoined twins who also share these structures in utero. ![]() The other theory, no longer believed to be the basis of conjoined twinning, is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find like-stem cells on the other twin and fuse the twins together. ![]() The more generally accepted theory is fission, in which the fertilized egg splits partially. Two contradicting theories exist to explain the origins of conjoined twins. Most live births are female, with a ratio of 3:1. Approximately half are stillborn, and an additional one-third die within 24 hours. An extremely rare phenomenon, the occurrence is estimated to range from 1 in 49,000 births to 1 in 189,000 births, with a somewhat higher incidence in Southeast Asia and Africa. X-ray of conjoined twins, cephalothoracopagus.Ĭonjoined twins are identical twins joined in utero. ![]()
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