The baby girl, who was born to Chinese mainland parents had to undergo surgery at just three weeks old to remove them.
The newborn baby was referred to Dr. Yu Kai-man, an obstetrician and gynecologist at Queen Elizabeth Hospital in Hong Kong, because the baby was suspected to have a tumor, according to the case report.
The mother's prenatal ultrasound had revealed an unusual mass within the infant, but it was unclear to the doctors exactly what the mass was. During surgery, which was done when the girl was about 3 weeks old, the surgeons discovered two fetuses between her liver and her kidney.
One fetus weighed 0.3 ounces (9.3 grams) and the other 0.5 ounces (14.2 grams) — corresponding to about 8 and 10 weeks' gestation, the case report said.
Each of the babies had an umbilical cord that linked to a placenta-like mass in the girl's belly.
Dr Yu Kai-man said: "It was almost impossible to detect during the prenatal check-up, as the embryo inside the baby was too small.
"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."
Though doctors describe the incident as unique, there can be other similar examples found in history.
A 36-year-old farmer had the embryo of his twin brother removed in the town of Nagpur, India, in 2006. The man asked for medical help only after his swollen belly hampered his breathing.
Doctors were certain that the man had a gigantic tumor in his belly. However, they found fragments of human genitalia, hairs, limbs and jaws in the patient and finally removed a weird underdeveloped creature having legs and arms with long nails.
In 2002, Indian doctors found a fetus in the body of a six-month-old boy. The dead fetus, which surgeons removed from the boy, weighed one kilo, whereas the boy himself weighed 6.5 kilos.
The anomalous phenomenon is known as fetus in fetu. Such incidents are extremely rare: an embryo inside an embryo may appear once in 500,000 pregnancies. The phenomenon always occurs at an early stage of pregnancy. As a rule, the fetuses die in mother's womb.
It may also happen that a child with a fetus inside survives the entire pregnancy. In this case the embryo continues to live inside its owner's body like a trapped parasite.
A 36-year-old farmer had the embryo of his twin brother removed in the town of Nagpur, India, in 2006. The man asked for medical help only after his swollen belly hampered his breathing.
Doctors were certain that the man had a gigantic tumor in his belly. However, they found fragments of human genitalia, hairs, limbs and jaws in the patient and finally removed a weird underdeveloped creature having legs and arms with long nails.
In 2002, Indian doctors found a fetus in the body of a six-month-old boy. The dead fetus, which surgeons removed from the boy, weighed one kilo, whereas the boy himself weighed 6.5 kilos.
The anomalous phenomenon is known as fetus in fetu. Such incidents are extremely rare: an embryo inside an embryo may appear once in 500,000 pregnancies. The phenomenon always occurs at an early stage of pregnancy. As a rule, the fetuses die in mother's womb.
It may also happen that a child with a fetus inside survives the entire pregnancy. In this case the embryo continues to live inside its owner's body like a trapped parasite.