Definition
Conjoined twins are an extremely rare type of identical twins who are physically joined at birth.
Description
Scientists believe conjoined twins form because of a delay in the fertilized egg's division. In normal identical
Conjoined twins are commonly referred to as Siamese twins, although this is now considered a derogatory term. The phrase Siamese twins originated from the famous conjoined twins Eng and Chang Bunker, who were born in Siam (Thailand) in 1811.
Some conjoined twins are attached at the upper body, others may be joined at the waist and share a pair of legs. Conjoined twins often share major organs such as a heart, liver, or brain. Medical experts have identified several types of conjoined twins. They are classified according to the place their bodies are joined. Most of the terms contain the word pagus, which means "fastened" in Greek.
Upper body
Cephalopagus: A rare form that involves conjoined twins with fused upper bodies and two faces on opposite sides of a single head.
Craniopagus: Conjoined twins with separate bodies and one shared head is a rare type and only occurs in 2% of cases.
Thoracopagus: About 35% of conjoined twin births have this common form of the condition, which joins the upper bodies. These twins usually share a heart, making surgical separation nearly impossible.
Lower body
Ischopagus: About 6% of conjoined twins are attached at the lower half of the body.
Omphalopagus: The type of conjoined twins that are attached at the abdomen and that often share a liver accounts for approximately 30% of all cases.
Parapagus: About 5% of conjoined twins are joined along the side of their lower bodies.
Pygopagus: About 19% of conjoined twins are joined back to back with fused buttocks.
