Cephalothoracopagus

Conjoined twins, popularly referred to as Siamese twins, are twins joined in utero. It is estimated to occur in anywhere between one in 50,000 births to one in 200,000 births, with a somewhat higher incidence in southwest Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1.