A baby born in Hong Kong was pregnant with her own siblings at the time of her birth, according to a new report of the infant's case.
The baby's condition, known as fetus-in-fetu, is incredibly rare, occurring in only about 1 in every 500,000 births. It's not clear exactly why it happens.
"Weird things happen early, early in the pregnancy that we just don't understand," said Dr. Draion Burch, an obstetrician and gynecologist in Pittsburgh, who goes by Dr. Drai. "This is one of those medical mysteries."
The World Health Organization considers a tiny fetus found within an infant to be a kind of teratoma, or tumor, rather than a normally developing fetus. (Seeing Double: 8 Fascinating Facts About Twins)
But the doctors who treated the baby girl wrote that rather than a teratoma, the tiny fetuses may instead be the remains of sibling twins that were absorbed during the pregnancy.
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.