Beijing: In an extremely rare medical occurrence, a pair of fetuses have been found inside the body of a newborn baby girl in Hong Kong, who has recovered from a surgery to remove the mass of tissue.
The fetuses were both joined to a placenta-like mass by umbilical cords. Each one had four limbs, skin, a rib cage, intestines and primitive brain tissue, according to a study published in the latest edition of the Hong Kong Medical Journal.
It was "one of those very rare things that make the world stand still," said Dr Nicholas Chao, one of the surgeons who operated on the baby.
The unusual condition, known as "fetus-in-fetu," is estimated to happen once in every half million births but has been reported less than 200 times worldwide, according to the study published by Chao and his colleagues in Hong Kong.
The baby was born in November 2010 to a mother from mainland China. The little girl recovered well from the operation to remove the mass of tissue, Chao was quoted as saying by CNN.
But uncertainty remains over how the two unusual entities ended up inside her.
The two forms had somewhat different weights but identical levels of organ development -- consistent with about 10 weeks of gestation.
They had spines, "ambiguous external genitalia" but no skulls.
The mother of the girl had reportedly had a normal ultrasound early in the pregnancy, suggesting that the other two fetuses "might have been tiny parasitic fetuses that had grown slowly" with the girl, according to the study.
That contrasts with the more popular theory of additional fetuses that develop normally early on and then get absorbed by the main fetus and stop growing.
The mass of tissue was spotted in a scan at 37 weeks. Further scans after the baby girl was born showed the mass between her spleen and left kidney, measuring nearly two inches across.