The girl, born to Chinese mainland parents in Queen Elizabeth Hospital Hong Kong, had to undergo surgery at just three weeks old to remove them.
The foetuses, 8 to 10 weeks gestated, had legs, arms, a spine, rib cage and intestines.
Both were also covered in skin one weighed 14.2 grammes and the other 9.3 grammes – and each had an umbilical cord.
The surgery was successful and the girl was discharged from hospital eight days later.
Doctors are yet to fully understand what causes the condition.
Dr Yu Kai-man, a specialist in obstetrics and gynaecology, said: ‘It was almost impossible to detect during the prenatal check-up, as the embryo inside the baby was too small.
‘Since it is impossible for the little girl to have conceived the pregnancy on her own, the fertilisation of the twin fetuses, of course, belongs to her parents, which has gone to the wrong place.’
The birth was reported in the Hong Kong Medical Journal which suggested it was possibly linked to the mother having multiple abortions.
Source: Metro UK
Picture: Hong Kong Medical Journal
