The twin within the twin.

When surgeons prepared to operate on 26-year-old Sanjay Kumar they expected to find an enormous tumour. But whensurgeon Ajay Mehta cut into the tumour he found instead a human hand, followed by other human body parts such as bones, hair and nails. This programme explains how such twin pregnancies can occur and examines various cases of traumatic twin pregnancies, in particular twin-twin transfusion syndrome (TTTS).