PHILADELPHIA

• The world’s oldest conjoined twins, Lori and George Schappell, recently died, aged 62.
• Conjoined twins are incredibly rare, accounting for about one or two in every 100,000 births.
• Because conjoined twins are so rare, it is difficult to know exactly how they come about.

Types of conjoined twins

• There are 15 recognised types of conjoined twins, based on the various places their bodies fuse.
• Conjoined twins are usually picked up on routine ultrasound scans performed during pregnancy.
• Conjoined twins who are diagnosed by imaging are typically delivered by caesarean section.

Separating twins

• One of the longest operations to separate conjoined twins, who were fused at the cranium, took more than 100 hours.
• The earliest recorded attempt at surgical separation of conjoined twins dates back to AD945 in Armenia where conjoined brothers lived until middle age before one of them died.
• Separating conjoined twins requires a significant amount of planning before surgery can begin, including, of course, lots of imaging such as ultrasound, CT and MRI.
• Twins who share vital organs – or whose organs are fused – have a lower chance of a successful separation.

Adam Taylor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.