Prognosis
More than 80% of hydatidiform moles are benign. The outcome after treatment is usually excellent. Close follow-up is essential to ensure that treatment has been successful. Highly effective means of contraception are recommended to avoid pregnancy for at least 6 to 12 months. Women who have had a prior partial or complete mole, have a slightly increased risk of a second hydatidiform mole in a subsequent pregnancy, meaning a future pregnancy will require an earlier ultrasound scan.In 10 to 15% of cases, hydatidiform moles may develop into invasive moles. This condition is named persistent trophoblastic disease (PTD). The moles may intrude so far into the uterine wall that hemorrhage or other complications develop. It is for this reason that a post-operative full abdominal and chest X-ray will often be requested. In 2 to 3% of cases, hydatidiform moles may develop into choriocarcinoma, which is a malignant, rapidly growing, and metastatic (spreading) form of cancer. Despite these factors which normally indicate a poor prognosis, the rate of cure after treatment with chemotherapy is high. Over 90% of women with malignant, non-spreading cancer are able to survive and retain their ability to conceive and bear children. In those with metastatic (spreading) cancer, remission remains at 75 to 85%, although their childbearing ability is usually lost. Epidemiology
Hydatidiform moles are a rare complication of pregnancy, occurring once in every 1,000 pregnancies in the US, with much higher rates in Asia (e.g. up to one in 100 pregnancies in Indonesia).
In approximately 20% of complete moles, the most probable mechanism is that an empty egg is fertilized by two sperm. In both cases, the moles are diploid (i.e. there are two copies of every chromosome). In all these cases, the mitochondrial genes are inherited from the mother, as usual. Most partial moles are triploid (three chromosome sets). The nucleus contains one maternal set of genes and two paternal sets. The mechanism is usually the reduplication of the paternal haploid set from a single sperm, but may also be the consequence of dispermic (two sperm) fertilization of the egg.In rare cases, hydatidiform moles are tetraploid (four chromosome sets) or have other chromosome abnormalities. A small percentage of hydatidiform moles have biparental diploid genomes, as in normal living persons; they have two sets of chromosomes, one inherited from each biological parent. Some of these moles occur in women who carry mutations in the gene NLRP7, predisposing them towards molar pregnancy. These rare variants of hydatidiform mole may be complete or partial. Diagnosis
The diagnosis is strongly suggested by ultrasound (sonogram), but definitive diagnosis requires histopathological examination. On ultrasound, the mole resembles a bunch of grapes ("cluster of grapes" or "honeycombed uterus" or "snow-storm"). There is increased trophoblast proliferation and enlarging of the chorionic villi, and angiogenesis in the trophoblasts is impaired.Sometimes symptoms of hyperthyroidism are seen, due to the extremely high levels of hCG, which can mimic the effects of thyroid-stimulating hormone.