Those fetuses reportedly each had four limbs, a spine, rib cage, intestines, anus, and an umbilical cord connected to a single placenta-like mass, but one fetus weighed
According to the South China Morning Post, the condition reported of the girl is extremely rare, occurs in only about 1 in 500,000 births, and fewer than
Dr Yu Kai-man, a specialist in obstetrics and gyneacology, explained fetus in fetu is a rare condition of external fertilisation embryo, and the fetus was unlikely to survive.
"It was almost impossible to detect during the prenatal check-up, as the embryo inside the baby was too small," said Yu, a former professor at Chinese University of Hong Kong.
The report said the reason behind the abnormality is still unknown, and that the World Health Organisation classified it as a variant of mature teratoma, a type of cancer.
But [the report] suggested [the condition] was possibly linked to the mother having multiple abortions. The report said that more evidence was needed to confirm either theory.
Dr Yu Kai-man also noted the newborn girl wasn't "pregnant" in the sense of carrying her own conceived children in her womb; she instead housed in her abdomen mislocated fetuses produced by her own parents' fertilization:
"Since it is impossible for the little girl to have conceived the pregnancy on her own, the fertilisation of the twin fetuses, of course, belongs to her parents, which has gone to the wrong place."
Last updated: 10 February 2015
Pang, Kristine KY et al. "A Case Report of a Twin Fetus-in-Fetu and a Revisit of the Known Rarity." Hong Kong Medical Journal. February 2015 21(1):80–3. Tsang, Emily. "Baby Born in Hong Kong Hospital Found with Twin Fetuses in her Abdomen." South China Morning Post. 7 February 2015.