Clinical meaning
A molar pregnancy, also known as hydatidiform mole, is a form of gestational trophoblastic disease (GTD) in which abnormal fertilization leads to the development of nonfunctional placental tissue instead of a viable embryo. The condition arises from errors in fertilization that produce an abnormal chromosomal complement in the conceptus. There are two distinct types: complete mole and partial mole. In a complete hydatidiform mole, an empty ovum (with absent or inactivated maternal chromosomes) is fertilized by one sperm that duplicates its chromosomal material, resulting in a 46,XX diploid karyotype that is entirely paternal in origin (androgenetic). Alternatively, two sperm may fertilize the empty ovum producing a 46,XX or 46,XY complement. In a complete mole, no fetal tissue develops; instead, all chorionic villi undergo hydropic swelling and form characteristic grape-like vesicles that fill the uterine cavity. The trophoblastic tissue proliferates excessively and produces extremely elevated levels of human chorionic gonadotropin (hCG), often exceeding 100,000 mIU/mL, which is far higher than normal pregnancy levels at equivalent gestational ages. In a partial hydatidiform mole, a normal ovum is fertilized by two sperm simultaneously,...