Fetus in fetu (or foetus in foetu ) is a developmental abnormality in which a mass of tissue resembling a fetus forms inside the body. There are two theories of origin concerning "fetus in fetu". One theory is that the mass begins as a normal fetus but becomes enveloped inside its twin .The other theory is that the mass is a highly developed teratoma . "Fetus in fetu" is estimated to occur in 1 in 500,000 live births. In India, Sanju Bhagat from Nagpur discovered he had Fetus in Fetu, which occurs when a twin grows inside the other sibling in the early stages of pregnancy and survives long after its birth, when he was 36. He always had an unusually large stomach, and finally got the twin removed, noting that it even had fingernails! https://en.m.wikipedia.org/wiki/Fetus_in_fetu
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