Lithopedions are bizarre, yet horrifying and sad results of fetuses dying in the womb. When a mother is carrying a dead fetus that she does not abort, miscarry or birth, it can calcify inside of her if it is too big for the body to reabsorb. It is a way that the human body can protect itself, as the dead fetus can cause infection. The resulting calcification leaves something akin to a stone fetus inside the mother. These sad remnants of a failed pregnancy are called lithopedions.

In most countries where medical care is readily available, lithopedions are unheard of. Dead fetuses are not left inside mothers and mothers are typically aware that they are pregnant. However, in places where many women do not have access to medical treatment, women may carry "stone babies" and not know it. Even if a woman does know she was pregnant and has a noticeable bulge, she can still carry it for decades without a problem, though there can be complications. Some women have even had healthy pregnancies after a lithopedion has formed. Without an ultrasound, there is no way of knowing that the womb is shared with a dead fetus and the dead fetus is not birthed with the live one.

Lithopedions are a thankfully rare occurrence, judging by known cases, though there are surely some that were never discovered. There has been an average of less than one known case per year for 400 years. A similar condition is fetus papyraceus, which occurs in multiples pregnancies when one of the fetuses flattens and mummifies. Lithopedions too can occur during multiples pregnancies. This condition is completely avoidable and reversible with proper medical treatment.