The rare phenomenon is known as a lithopedion, also referred to as a "stone baby."
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A 91-year-old woman from the small town of La Boca, Chile, recently found out she's been carrying a calcified fetus in her abdomen for more than half her life.

According to CNN, Estela Meléndez felt a lump on her abdomen for years. But it wasn't until she visited a local clinic this summer, after suffering a fall, that she learned it was a fetus all along.

Doctors there ordered an X-ray that showed what at first seemed to be a large tumor. A second X-ray was done to confirm the findings before a team performed surgery, and that's when doctors realized the mass was actually a calcified fetus that had likely been in the woman's body for more than six decades.

The rare phenomenon is known as a lithopedion, also referred to as a "stone baby," and typically occurs when a fetus dies during an abdominal ectopic pregnancy. (That's when a pregnancy occurs outside of the womb, in the abdomen.) When the fetus dies, sometimes it's early enough that the woman's body can re-absorb it, but if it's too big, the mother's body will begin to encase the fetus in calcification to protect the body from the foreign object and possible infection. Over time, the calcified fetus becomes "mummified."

The fetus poses no health risk to Meléndez. But sadly, it likely prevented her from having children with her husband of more than 70 years, Manuel González, who passed away in January at the age of 91. "We suffered tremendously because of this reason," Meléndez explained to CNN.

Doctors considered performing surgery to remove the fetus, but ultimately decided that operating on a 91-year-old patient posed more risk than leaving it alone. Meléndez told CNN that the spot on her belly hurts occasionally, but most of the time it’s just an uncomfortable bump.