The exact incidence of molar pregnancy in various populations is not possible to ascertain because most epidemiologic studies have not separated complete from partial moles. The current classification of GTD is shown in Table 1 . A complete mole forms often a bulky mass, sometimes consisting of over 500 cc of bloody tissue, and has a classical bunch of grapes appearance. An embryo or fetus is absent. Histologically, all the villi are distended, edematous and often show central cisterns.
Fetal vessels are generally absent.
Cytogenetic analysis of complete moles has shown a 46,XX chromosomal constitution. Ultrasonography discloses a snowstorm appearance . The partial mole differs from the complete mole in that the volume of the tissue is often less than 300 cc and only a proportion of the villi are vesicular. It is not uncommon for a fetus to be present, and it may be abnormal. Histologically a proportion of the villi are edematous with sometimes a central cistern.