Identical twins are formed from a single egg and sperm that, a few days after fertilization, randomly form two or more embryos. When this separation occurs later, in the middle of the tenth day, pregnancy may be unfeasible; or, in very rare cases, conjoined twins form – often from one in 200,000 births.
Also called Siamese twins, united or bonded; these are linked by a common region of the body and may share one or more organs. When the union takes place through the thorax, they are called xiphopagus. Through the sternum, sternopagus. On the other hand, through the pelvis, they are the ischiopagus; and for the head, the so-called cephalopagus. Those joined by the face are called Metoppagos; on the back, rachiopagus; and those connected by the thorax, thoracopagus.
Depending on the organs these twins have in common, it may be possible to separate them surgically. However, this process is very delicate, does not always guarantee the survival of both children and can leave physical sequelae.
Curiosity:
The name “Siamese”, attributed to the twins united together, refers to Siam (present-day Thailand): birthplace of the brothers Chang and Eng. Linked by the thoracic region, these “Siamese twins”, as they became known, performed circus performances in the United States, making them well known. They lived for 63 years: period that lasted from 1811 to 1874; and who had the opportunity to marry and have a total of 21 children.
By Mariana Araguaia
Graduated in Biology
Source: Brazil School - https://brasilescola.uol.com.br/biologia/gemeos-coligados.htm
