'fetus in fetu' condition wherein babies are born pregnant
Computed Tomography scan of the patient, suffering from the 'fetus in fetu'.Wikimedia Commons/ Nisreen M Khalifa

Fetus in fetu (or foetus in foetu) is an extremely rare condition of developmental abnormality, defined as a monozygotic twin being incorporated into the abdomen of its sibling, during development, reports a research published in BMC Pediatrics.

Doctors are not sure of what might be the exact reason behind the condition. But, one theory is that the mass begins as a normal fetus but envelops inside its twin. It is so rare that roughly 200 cases have been reported worldwide.

Such an incident was recently reported in India, where a seven-month-old baby was born with a fetus growing inside her. The parents of the baby girl, Prinsa Rathava noticed a lump growing rapidly on her tiny body.

The parents, who were extremely worried, took Prinsa to a hospital where a 130g fetus was found between the intestines and kidneys of the little girl.

Doctors operated on her at Civil Hospital in Gujarat, India and removed the malformed fetus on February 19. Doctors said that the child should grow into a healthy adult.

"In this case, the undeveloped fetus had a normal vertebrae column, brain tissues, head, limb buds and an anal dimple," the head of the department of pediatric surgery, Dr. Rakesh Joshi told The Indian Express. "The parents of the child noticed a lump like structure in the child but ignored it. This happened when the child was five months old."

He added: "Since the lump was growing at an alarming rate, the parents got it checked in Baroda and then came to our hospital."

Prinsa was admitted to the hospital on February 15. A team of six operated on the little girl including three senior anesthetists.

Dr. Joshi said: "There will be no future complications in the case and she will grow up normally. The surgery was tough as the undeveloped fetus was behind the intestine and between both the kidneys."

He added: "The formation is caused by the incomplete separation of twins, which fails to grow and instead becomes an internal part of the healthy twin."