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Conjoined twins

  Oct 31, 2017

Conjoined twins

A pair of conjoined twins from Odisha have been successfully separated by doctors. The feat was achieved in a marathon surgery at the All India Institute of Medical Science (AIIMS).

The surgery presented a peculiar challenge because babies were attached at the skull. This condition is called carniopagus conjoining. The twin shared brain tissue, nerves and major blood vessels. The operation lasted 16 hours and involved 40 surgeons and specialists. It is the first case of craniopagus twins being separated in the country. The chances of their survival were 10-15%, which is the same as the global average.

Fifty-nine such craniopagus surgeries have been performed worldwide. Separation surgeries for two other sets of craniopagus twins – one from Hyderabad and another from Patna were planned in India in the past, but abandoned because the risks were too high.

Conjoined twins are identical twins joined in utero. An extremely rare phenomenon, the occurrence is estimated to range from 1 in 49,000 births to 1 in 189,000 births, with a somewhat higher incidence in Southeast Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1.

Two contradicting theories exist to explain the origins of conjoined twins. The more generally accepted theory is fission, in which the fertilized egg splits partially. The other theory, no longer believed to be the basis of conjoined twinning, is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find like-stem cells on the other twin and fuse the twins together. Conjoined twins share a single common chorion, placenta, and amniotic sac, although these characteristics are not exclusive to conjoined twins as there are some monozygotic but non-conjoined twins who also share these structures in utero. Craniopagus twins are conjoined twins that are fused at the cranium. Additionally, conjoined twins are genetically identical and always share the same sex.