According to University of Maryland Medical Center, between
40 to 60 percent of conjoined twins are stillborn, and few survive past infancy. Interestingly,
female siblings reportedly have a greater chance of survival than males, and according to the publication, they are three times more likely to be born alive. And one of the first known cases of conjoined female twins occurred in England in 1100, when two sisters, Mary and Eliza Chulkhurst, were born joined at the hip. But the most famous conjoined twins in history where Chang and Eng Bunker who were born in Thailand in 1811 (which was known as Siam at the time)—both were married, and between them, they fathered 21 children.
There is not just one type of conjoined twin either, but several, based on where they are joined. For example, the extremely rare cases are joined at the head, which is referred to craniopagus (brain, meninges) twins, while thoracopagus (heart, liver, intestine) twins are reportedly the most common.
The surgical process of separating conjoined twins is incredibly complicated and risky (depending on the type of connection they share and whether or not they share organs). However, over the years, medical experts have become increasingly capable of separating pairs of conjoined twins, and many have gone on to live normal, individual lives. However, one of the most well-known cases of conjoined twins in the last decade that cannot be separated is Abby and Brittany Hensel, two (now adult) females who share a body but have separate heads.
The reason they cannot be separated is that they share a mix of individual and shared organs, with some of the vital shared organs including one set of reproductive organs, one liver, one small and large intestine and one diaphragm. Although according to Ranker, doctors did initially offer to attempt to separate the girls at birth, there was a high chance that one of the twins would die during the procedure, which led their parents to refuse the surgery.
Each girl controls one side of the body (Abby the right, and Brittany the left) which makes movement incredibly difficult and takes extreme coordination. But these women are quite amazing and have gone on to graduate from university with two degrees in education.