Out of the 30 pygopagus
cases reported worldwide, 26 were female and only four were male.
Conjoined twins represent an uncommon congenital malformation, with an estimated incidence of 1: 50,000-1: 100,000,1 and approximate 75 Percent of cases are females.2,3 Usually, conjoined twins are classified according to the most prominent site of conjunction: thorax (thoracopagus) 40 Percent , abdomen (xiphopagus and omphalopagus) 33 Percent , sacrum (pygopagus
) 18 Percent , pelvis (ischiopagus) 6 Percent , and craniopagus (1-2 Percent).3,4
The more common types of conjoined twins include the thoracopagus type where the fusion is anterior, at the chest, and involves the heart (35%); the omphalopagus type where the fusion is at the mid-trunk (30%); the pygopagus
type where there is a posterior union involving the rump (19%); the parapagus type, with a lateral fusion of the lower half of the body extending upwards (5%); and combination types.
Conjoined twins are classified according to the most prominent site of conjunction: thorax (thoracopagus); abdomen (omphalopagus); sacrum (pygopagus
); pelvis (ischiopagus); skull (cephalopagus), side by side (parapagus) and back (rachipagus).