The cause of the abnormalities is unknown but the World Health Organisation classified it as a type of cancer.
A baby girl was born in 2010 and found to be pregnant with twins in Hong Kong.
The girl who was born in Queen Elizabeth Hospital had to undergo surgery at just three weeks old to remove them.
The extraordinary goggling incident was detailed in the latest edition of the Hong Kong Medical Journal.
According to the report, the condition which is known as foetus in foetu occurs in just one in 500,000 births in the world.
The 10-week old gestated foetuses had legs, arms, a spine, rib cage, intestines and were also covered in skin.
Both foetuses which had umbilical cord, weighed 14.2 grammes and the other 9.3 grammes .
The surgery was successful and the girl was discharged from hospital eight days later.
According to UK Mirror, it is believed that this case is the first to be documented in the city.
"It was almost impossible to detect during the prenatal check-up, as the embryo inside the baby was too small," Dr Yu Kai-man, a specialist in obstetrics and gynaecology, said.
"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," said Yu, a former professor at Chinese University of Hong Kong.
According to report, the cause of this abnormality has not been determined but the World Health Organisation classified it as a type of cancer and suggested it was possibly linked to the mother having multiple abortions.