BOGOTA (REUTERS) - Colombian doctors trying to remove a suspected tumor from the abdomen of a 4-month-old baby instead discovered a well-formed fetus - possibly the baby's twin. Staff at the Rafael Urbina clinic in Cali, 155 miles (250 km) southeast of Bogota, said the rare discovery was made during an operation on Monday on a baby boy with a swollen midriff. "The child is recovering well, although he needed a blood transfusion after the fetus had been removed," a pediatric nurse at the clinic told Reuters. Doctors said it was the first case in Colombia of a medical condition known as "fetus in fetus" and one of less than 100 worldwide. "You could see its feet, a slightly-deformed skull ... a poorly-defined face, back and genitals," Dr. Freddy Orozco, who took part in the operation, was quoted as saying by El Espectador newspaper on Friday. "It wasn't alive as such, its heart wasn't beating, but it did have live tissue because its hair was growing," he said. Doctors said the six-inch (15-cm) long embryo had survived by attaching itself to a vein within the baby's intestines. The most probable theory, they said, was that the fetus was a twin absorbed by the other inside the mother's womb.