The newborn is only three weeks old and removing the fetuses out of her tiny body is necessary. The said condition was the first documented case of "Fetus in fetu" in Hong Kong. The twins inside her were obviously not hers as they were only fertilized eggs that was absorbed into her body while development stage in the womb is taking place. At first, the mother was suspected to be pregnant with triplets. But the surviving baby absorbed her siblings inside herself. Both fetuses had four limbs, a spine, rib cage, intestines, and anus.
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. - wikipedia
“Since it is impossible to the little girl to have conceived the pregnancy on her own, the fertilization of the twin fetuses, of course, belongs to her parents, which has gone to the wrong place. It was almost impossible to detect during the prenatal check-up, as the embryo inside the baby was too small,” - Dr. Yu Kai-man
The causes for "Fetus in fetu"can be attributed to the mother having more than one abortion. A non-cancerous tumor containing tissue, hair, and even teeth called teratoma could also be the causative factor to this condition.