A lithopedion, or "stone fetus," is usually the result of an extrauterine (abdominal or ectopic) pregnancy. Extrauterine pregnancies generally end in rupture of the fallopian tube, miscarriage, or absorption of the fetus, but in the rare cases (about 0.0045% of pregnancies) where none of these occur, the fetus may remain in the body and calcify. Fetuses that become lithopedia are occasionally lodged in the ovaries or vagina rather than in the uterus or fallopian tubes.

A fetus large enough to avoid expulsion or absorption takes a long time to accumulate enough calcium deposits that it turns to stone. Lithopedia have been extracted from women as old as 94, who have been unknowingly carrying the fetuses for upwards of 60 years. Serious complications like intestinal obstruction can result from lithopedion formation, but many cases are stable for a very long time, sometimes going unnoticed for decades. Often the lithopedion is initially misdiagnosed as a cyst or tumor, and is only shown to be a calcified fetus upon removal.

The physician Albucasis was the first to document the lithopedion phenomenon, in his 11th century treatise on surgery. In 1557, physician Israel Spach included in his gynecological text an illustration of a lithopedion in situ (that is, inside a woman's opened womb). He appended this caption: "Deucalion cast stones behind him and thus fashioned our tender race from the hard marble. How comes it that nowadays, by a reversal of things, the tender body of a little babe has limbs nearer akin to stone?" Spach apparently considered the lithopedion to represent a reversion to (mythical) early forms of humanity, in something like the way that Ernst Haeckel would later see the early evolution of man reflected in the fish-like fetus.

Lithopedia are less common in developed countries with adequate health care, since pregnancies that are neither carried to term nor obviously terminated are not likely to go unnoticed.

Around page 9 of my Google search, I started turning up PORN SITES. I do NOT want to ask what "lithopedion" has to do with "Free XXX Nun Sex," "Fat Italian Women Nude," or "Gay Twinks Fucked Till They Bleed." I shit you not.