Amniotic tissue in complete hydatidiform moles can be androgenetic

The purpose of this study was to determine whether amniotic tissue found associated with cases of complete hydatidiform mole (CM) was genetically identical to the CM, and therefore part of the molar pregnancy, or genetically dissimilar to the CM, suggesting derivation from a twin pregnancy. DNA was prepared from formalin-fixed, paraffin-embedded blocks of tissue containing both CM and amnion. Maternal DNA was prepared from decidual tissue in the same blocks, or from a maternal blood sample. Fluorescent microsatellite genotyping was carried out to determine the origin of both the CM and the amniotic tissue. In one of six cases examined, the amniotic tissue was genetically different from the CM and was therefore likely to be derived from a twin pregnancy. In the five remaining cases, the amniotic tissue was genetically identical to the CM and was likely to be derived from the same conceptus. It is concluded that androgenetic CM can support the development of amniotic tissue and that some early embryonic development may occur in CM. The presence of amnion, or other fetal tissues, associated with molar tissue should not therefore always be considered indicative of a diagnosis of partial mole (PM).