Overview
Clinical Meaning
A molar pregnancy, also called a hydatidiform mole, is a form of gestational trophoblastic disease caused by abnormal fertilization.
A molar pregnancy, also called a hydatidiform mole, is a form of gestational trophoblastic disease caused by abnormal fertilization. Trophoblastic tissue proliferates abnormally instead of developing into a viable pregnancy. The two forms are biologically different. In a complete hydatidiform mole, an ovum lacking maternal nuclear DNA is fertilized by one sperm that duplicates its chromosomes or by two sperm. The result is a diploid, entirely paternally derived karyotype; approximately 90% are 46,XX. No fetal tissue develops. Instead, all chorionic villi become hydropically swollen and may form grape-like vesicles within the uterine cavity. This extensive trophoblastic growth produces very high human chorionic gonadotropin (hCG) levels. In a partial hydatidiform mole, a normal ovum is fertilized by two sperm or by a diploid sperm. The result is usually triploid: 69,XXY, 69,XXX, or 69,XYY. Abnormal fetal tissue may be present, but it cannot develop into a viable infant. Hydropic villous changes are more limited, and hCG is often lower than with a complete mole. The clinical pattern follows the amount of trophoblastic tissue and hCG activity. First-trimester vaginal bleeding and a uterus...