A molar pregnancy occurs when the fertilisation of the egg by the sperm goes wrong and leads to the growth of abnormal cells or clusters of water filled sacs inside the womb. This condition is one of a group of conditions known as gestational trophoblastic tumours (GTTs). Molar pregnancies used to be called hydatidiform mole but now most people call them molar pregnancies. Most molar pregnancies are benign (not cancerous). They can spread beyond the womb in some women, but are still curable.
Complete molar pregnancy – when the egg with no genetic information is fertilized by a sperm or when the nucleus of an egg is either lost or inactivated. The sperm grows on its own, duplicates itself because the egg was lacking genetic information but it can only become a lump of tissue. It cannot become a foetus. Usually there is no foetus, no placenta, no fluid and no amniotic membranes. As this tissue grows, it looks a bit like a cluster of grapes. This cluster of tissue is called a mole and it can fulfil the uterus. The uterus is rather filled with the mole that resembles a bunch of grapes.
All women of reproductive age who have previously been, or are currently pregnant, are at risk of GTD, however women younger than 16 or older than 40 who become pregnant are more likely than women aged 16-39, to develop a molar pregnancy. An estimated 1-3 in 1000 pregnancies are affected by benign hydatidiform moles; however incidence varies internationally and is highest in the Asian region. Some 10% of all hydatidiform moles will become malignant; an estimated 8-15% of complete and 1.5-6% of partial hydatidiform moles.