In 1880 Dr. Friedrich Kuchenmeister and Dr. Tein preformed a review of past and present cases of lithopedions. The two doctors were able to define three subgroups of lithopedion formation with calcification, which later in time the medical community adhered to their classification. In the lithokelyphos, or stone sheath category, calcification occurs mainly in the membranes of the yolk sac or placenta, and does not involve the fetus itself. In true lithopedion, the fetus itself is infiltrated with calcium salt deposits after it is deposited into the abdominal cavity from rupture of the membranes. Finally in the lithokelyphopedion group, the fetus and the yolk sac/placenta are completely calcified inside and out (Mondofacto, 2001). Of Dr. Tein’s large lithopedion groups, all of the patients fell under one of these three categories. Of 114 Lithopedion cases, 74 were the results of ectopic pregnancies, while 13 originated in ovarian pregnancies (which are an ectopic pregnancy that occurs in the ovaries). These lithopedions were located in the abdominal cavity after the rupture of the uterus. Eight lithopedions were a result of primary abdominal pregnancies (in which the fertilized egg attaches to an abdominal organ and develops to a certain point until calcification takes place) (Britannica, 2011). Five lithopedions originated in the horn of a bicornuate uterus (bicornuate uterus is a deformed uterus which look like horns, in which many pregnancy cannot be sustained) (Bondeson, 2000). The fetal age of the lithopedion is often difficult to estimate due from drying up and shrinking of the fetus. It should be noted, however, that 43 percent of the cases were described as being the size of a fetus at full term. The bulk of these cases are from the 1500-1900 time periods. It is very rare to see any of these cases in today’s society.