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A woman in Colombia gave birth to a baby girl whose abdomen housed the tiny body of her own twin sister, according to a report by the The New York Times.

The phenomenon is called a "fetus-in-fetus" and although extremely rare, it has happened previously. The Times reports that this type of birth was described in a British medical journal in 1808 and has happened more recently in India, Indonesia and Singapore.

Dr. Miguel Parra-Saavedra, a high-risk pregnancy specialist in Baranquilla, Colombia first saw the mother, Monica Vega, five weeks before she was due to give birth, the Times said. Vega was referred to him because her obstetrician thought her fetus had a cyst on its liver.

Instead, Dr. Parra-Saavedra discovered that the "cyst" was actually a tiny infant with its own umbilical cord that took nourishment from the larger infant.

“I told the mother, and she said, ‘What? No, doctor, this is impossible,’" Dr. Parra-Saavedra said, according to the Times. “But I explained step by step, and she understood.”

Vega delivered her baby on February 22 by Caesarean section and the next day, doctors performed laparoscopic surgery on the newborn infant, Itzamara, to remove the fetal twin.

Dr. Parra-Saavedra said that the fetal twin was two inches long and had a partially formed head and limbs but no brain or heart.

According to the Times, doctors believe that the fetus-in-fetus condition forms when twin embryos fail to completely divide and the larger one then wraps around the smaller one. Since the smaller fetus takes nourishment from the bigger one, it is called a parasitic twin.

Dr. Parra-Saavedra said that Izamara is doing well, the Times reported. “She has a little scar on her abdomen, but she is a normal baby now except that the whole world is talking about her.”