Doctors say that the bizarre condition is an example of an extremely rare developmental abnormality called fetus-in-fetu, whereby a tiny fetus (or fetuses) develops within the body. It's not entirely clear what causes it, but it is believed to occur in about 1 out of every 500,000 births.
Though the World Health Organization typically categorizes fetuses growing inside of infants as tumors, this condition is different. Both of the tiny fetuses were found between the baby girl's liver and a kidney, and each were attached to an umbilical cord that linked to a placenta-like mass in the girl's belly. The fetuses were incapable of developing due to their abnormal situation — and obviously the baby girl would not have been capable of bringing them to term.
It is believed that the baby began as one of triplets, but for some reason the two undeveloped fetuses just became absorbed into the body of the remaining child. Thus, doctors guess that the two tiny fetuses are actually the baby girl's own siblings.
"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."
As strange as this condition sounds, the developed child can grow up normally even if the tiny fetuses are not detected and removed upon birth. For instance, an 18-year-old boy had his retained twin removed in a major surgery in 2011.
In an unrelated, though similarly bizarre condition, fetuses that die in utero can become calcified and turned into stone. These fetuses, sometimes called "stone babies," are not always detected until years later. In 2014, a 60-year-old woman who originally visited her doctor complaining of abdominal pain had to have a stone baby removed. She had been carrying it for 36 years.
The baby girl born with the twin fetuses had a successful surgery to remove the fetal masses, and she should grow up to live a normal life.
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