The rare medical condition was recorded by doctors in Israel earlier this month, according to a report by The Times of Israel on Wednesday, July 28.
The case referred to as "fetus-in-fetu" occurred at Assuta Medical Center in Ashod, Israel.
Medical officials have reportedly said that it was a 1-in-500,000 medical rarity.
The news outlet quoted Omer Globus, director of neonatology at the hospital as saying: "We were surprised to discover that it was an embryo."
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Before the baby was born, medical checks and ultrasound examinations of her mother had shown that the child had a large stomach.
It was then confirmed after her birth that she had a twin embryo inside her stomach.
The baby reportedly underwent ultrasound examinations and an X-ray before doctors removed two more formations from inside her stomach.
She is reportedly recuperating and is expected to make a full recovery soon. She has been discharged together with her mother.
Explaining the circumstances that lead to "fetus-in-fetu", Omer Globus Globus said there are several factors one of which involves the pregnancy starting as twins but one of the embryos is absorbed by the other.
“It happens as part of the fetal development process when there are cavities that close during development and one of the embryos enters such a space.
“The fetus inside partially develops but does not live and remains there,” the medical director said.