Home > Encyclopedia of Genetic Disorders > Conjoined twins

Definition

Conjoined twins are an extremely rare type of identical twins who are physically joined at birth.

Description

Scientists believe conjoined twins form because of a delay in the fertilized egg's division. In normal identical twins, the egg splits at four to eight days after fertilization. In conjoined twins, however, the split occurs sometime after day 13. Instead of forming two separate embryos, the twins remain partially attached as they develop inside the womb. In most cases, conjoined twins do not survive more than a few days past birth because of a high rate of malformed organs and other severe birth abnormalities. However, surgical separations have been successful in conjoined twins that have a superficial physical connection.

Conjoined twins are commonly referred to...