only about 10% of the incidence of hydatidiform mole. The reported incidence of GTD from Europe and North America is significantly lower than the reported incidence of GTD from Asia and South America. One proposed reason for this great geographical variation is differences in healthy diet in the different parts of the world (e.g., carotene deficiency). However, the incidence of rare diseases (such as GTD) is difficult to measure, because epidemiologic data on rare diseases is limited. Not all cases will be reported, and some cases will not be recognised. In addition, in GTD, this is especially difficult, because one would need to know all gestational events in the total population. Yet, it seems very likely that the estimated number of births that occur at home or outside of a hospital has been inflated in some reports. Terminology Gestational trophoblastic disease (GTD) may also be called gestational trophoblastic tumour (GTT). Hydatidiform mole (one type of GTD) may also be called molar pregnancy. Persistent disease; persistent GTD: If there is any evidence of persistence of GTD, usually defined as persistent elevation of beta hCG (see «Diagnosis» below), the condition may also be referred to as gestational trophoblastic neoplasia (GTN). See also Trophoblastic neoplasms References External links Germ cell neoplasia Health issues in pregnancy Rare diseases