Molar pregnancies are characterized by gross water logging and villous cistern formation. Villous trophoblastic hyperplasia is the microscopic characteristic feature of true molar pregnancies. This chapter reviews the role of ultrasound in early pregnancy in the screening for molar pregnancy. Complete moles are almost always diploid with their chromosomes totally derived from the paternal genome resulting from endoreduplication after monospermic fertilization or more rarely dispermic fertilization of an anucleate oocyte. Usually, the ultrasonographic description of complete hydatidiform moles (CHM) applies to pregnancies between 9 and 12 weeks of amenorrhea. In early pregnancy and in particular in missed miscarriage, independently of the presence of a chromosomal abnormality, the progressive disappearance of the villous vasculature after embryonic death leads to villous hydrops. Overall, the risk of persistent Gestational trophoblastic disorder (pGTD) developing from a histologically confirmed non-molar hydropic miscarriage is considered to be less than 1 in 50,000.