Molar Pregnancy: Abnormal Form of Pregnancy

Molar pregnancy is an abnormal form of pregnancy in which a non-viable fertilized egg implants in the uterus and converts a normal pregnancy into an abnormal one (which will fail to come to term). A molar pregnancy is a gestational trophoblastic disease[1] that grows into a mass in the uterus that has swollen chorionic villi. These villi grow in clusters that resemble grapes.[2] 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).[3] 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) [4] The genotype is typically 46,XX (diploid) due to subsequent mitosis of the fertilizing sperm, but can also be 46,XY (diploid).[4] 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 (tetraploid).[4] Complete hydatidiform moles have a higher risk of developing into choriocarcinoma — a malignant tumor of trophoblast cells — than do partial moles.
The etymology is derived from hydatisia (Greek "a drop of water"), referring to the watery contents of the cysts, and mole (from Latin mola = millstone/false conception).[5] The term, however, comes from the similar appearance of the cyst to a hydatid cyst in an Echinococcosis.[6]
A hydatidiform mole conception may be categorized in medical terms as one type of non-induced (natural) "missed abortion"[7] - referred to colloquially as a "missed miscarriage", because the pregnancy has become non-viable (miscarried) but was not immediately expelled (therefore was