Conjoined twins are identical twins joined in utero. 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, Africa and Brazil. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1. Most stillborns are male.