An abnormal pregnancy that probably results from the fertilization of a so-called empty egg, an egg without chromosomes. In this condition, the fertilized egg degenerates, and the placenta grows into a mass of tissue resembling a cluster of grapes. Molar pregnancy is very rare, occurring in only one out of every 1,000 or 1,200 pregnancies.
Pregnancy in which, instead of the ovum developing into an embryo, it develops into a mole.
A molar pregnancy arises when a tumor forms from placental tissue, and the embryo fails to develop properly. This type of pregnancy can be either noncancerous, known as a hydatidiform mole, or it can infiltrate the uterine wall, referred to as an invasive mole. If a molar pregnancy progresses to become cancerous, it is termed a choriocarcinoma.
When the deceased embryo and placenta remain within the uterus following a miscarriage, they give rise to a mass known as a carneous mole.