Page created on June 8, 2021. Last updated on January 17, 2022 at 15:22
Definition and epidemiology
Hydatidiform mole or molar pregnancy is a benign type of gestational trophoblastic disease, a condition caused by abnormal proliferation of trophoblasts. It’s characterised by transformation of terminal villi into vesicles filled with clear viscid material, making them look like grapes.
Hydatidiform moles are usually benign, but malignant in 15 – 25% of cases. In this case, it persists after removal of the neoplasm and is therefore called a persistent trophoblastic neoplasia (PTN).
Hydatidiform moles are curable in virtually 100% of cases, with fertility remaining intact. In cases of twin pregnancies where only one placenta becomes a molar pregnancy, the other baby can be born normally.
Gestational trophoblastic disease occurs in approx 1 in 1000 pregnancies.
- Old age
- Previous gestational trophoblastic disease
- Pathologic eggs
- Vitamin A deficiency
- Dietary protein deficiency
We can distinguish complete and partial hydatidiform moles. Moles are partial if normal placental tissues or foetal structures are present. If there are no such tissues present, it’s complete.
Complete moles are diploid and are the result of paternal disomy. A sperm cell (23X) duplicates itself after fertilisation of an empty egg, which forms the 46XX mole. It can also occur if two sperm cells fertilise an egg simultaneously, but that is very rare.
Partial moles are triploid. They occur when a normal egg is fertilised by two sperms simultaneously, forming either 69XXX, 69XXY, or 69XYY.
Complete moles are more likely to become malignant. Moles produce hCG, and at a higher level than what’s normal.
The patient considers themselves to be pregnant, due to the hCG-mediated symptoms of pregnancy like amenorrhoea and nausea. Symptoms of pregnancy may be more severe than what’s normal. The patient may also experience bright red spotting or dark brown vaginal discharge.
Severely elevated hCG can cause hyperthyroidism, due to hCG’s structural similarity to TSH and TSH-like effects.
Diagnosis and evaluation
On ultrasound, the uterus is enlarged compared to the gestational age. Bilateral enlarged ovaries with theca lutein cysts may be present. Ascites and pleural fluid may be present due to ovarian hyperstimulation.
The ultrasound picture of the mole itself is very characteristic, it’s described as being similar to snowfall. No foetus is seen.
The hCG concentration is significantly higher than normal, and no foetal vital signs can be detected.
The uterus should be evacuated as soon as possible. This is achieved by dilation of the cervix, followed by suction and curettage. Oxytocin infusion is used to prevent bleeding. After surgical removal, pathological evaluation is necessary to confirm the diagnosis.
If a mole is diagnosed over the age of 40, due to the high malignant potential, total abdominal hysterectomy should be performed.
Serum β-hCG must be monitored for 6 months after the treatment to make sure there is no persistence. Normalisation of the values may take months. If the values stop decreasing, or they start increasing, peristance is likely (persistent trophoblastic neoplasia). This is treated with methotrexate.