Conjoined twins are identical twins joined in utero. A 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 a smaller fraction of pairs born alive have abnormalities incompatible with life. The condition is more frequently found among females, with a ratio of 3:1.Two contradicting theories exist to explain the origins of conjoined twins.