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%).
Perhaps the most famous pair of conjoined twins were Chang and Eng Bunker (1811-1874), Chinese brothers born in Siam, now Thailand.
They traveled with P.T.
Barnum's circus for many years and were billed as the Siamese Twins; due to their notoriety and the rarity of the condition, today the term is frequently used as a synonym for conjoined twins.
Chang and Eng were joined by a band of cartilage at the chest (xiphopagus).
In modern times, they could have been separated easily.