 thumb|hydatidiform mole on ct, sagittal view thumb|hydatidiform mole on ct, axial view molar pregnancy is an abnormal form of pregnancy in which a non-viable fertilized egg implants in the uterus and will fail to come to term. a molar pregnancy is a gestational trophoblastic diseasegestational trophoblastic disease at american cancer society. last medical review: 04/14/2011 that grows into a mass in the uterus that has swollen chorionic villi. these villi grow in clusters that resemble grapes. a molar pregnancy can develop when an egg that is missing its nucleus is fertilized and that may or may not contain fetal tissue. it is characterized by the presence of a hydatidiform mole (or hydatid mole, mola hydatidosa). molar pregnancies are categorized into partial and complete moles. mole as used here simply indicates clump of growing tissue, or a 'growth'. a complete mole is caused by a single (90%) or two (10%) sperm combining with an egg which has lost its dna (the sperm then reduplicates forming a "complete" 46 chromosome set)  the genotype is typically 46,xx (diploid) due to subsequent mitosis of the fertilizing sperm, but can also be 46,xy (diploid). 46,yy (diploid) is not observed. in contrast, a partial mole occurs when an egg is fertilized by two sperm or by one sperm which reduplicates itself yielding the genotypes of 69,xxy (triploid) or 92,xxxy ([[
Germ_cell_neoplasia Pathology_of_pregnancy,_childbirth_and_the_puerperium Pregnancy_with_abortive_outcome