A Chinese girl was born pregnant with twin baby fetuses in her abdomen.

Although originally believed that the baby girl had two tumors in her abdomen, it was later discovered they were fetuses -- an abnormality known “fetus in fetu,” the South China Morning Post reported.

Fetus in fetu reportedly occurs in just one in 500,000 births in the world, and less than 200 cases have been reported.

Doctors performed surgery to remove the fetuses from her abdomen at 3-weeks-old. One of the fetuses weighed 14.2 grams, and the other 9.3 grams. Each was connected to a placenta-like mass by an umbilical cord.

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The fetuses’ gestation was around 8 to 10 weeks, and each had four limbs, a spine, a rib cage, intestines and anus. Both were covered in skin, the Daily Mirror reported.

This was reportedly the first documented case of fetus in fetu in Hong Kong, China.

"It was almost impossible to detect during the prenatal check-up, as the embryo inside the baby was too small," Dr. Yu Kai-man, an obstetrics and gynecology specialist, said.

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“Since it is impossible for 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.”

News of the medical anomaly was ultimately published in the Hong Kong Medical Journal.

The World Health Organization classified the abnormality as mature teratoma, a type of cancer, but it was suggested that it might have been linked to the mother having multiple abortions. Additional evidence is needed to prove either theory, according to the South China Morning Post.

Sources: Daily Mirror, South China Morning Post / Photo credit: Daily Mirror