Molar Pregnancy

A hydatidiform mole is a type of tumour that grows like a pregnancy inside the uterus. This is called a molar pregnancy. There are two types of molar pregnancy: a complete mole and a partial mole.

complete mole occurs when two sperm cells fertilise an ovum that contains no genetic material (an “empty ovum”). These sperm then combine genetic material, and the cells start to divide and grow into a tumour called a complete mole. No fetal material will form.

partial mole occurs when two sperm cells fertilise a normal ovum (containing genetic material) at the same time. The new cell now has three sets of chromosomes (it is a haploid cell). The cell divides and multiplies into a tumour called a partial mole. In a partial mole, some fetal material may form.



Molar pregnancy behaves like a normal pregnancy. Periods will stop and the hormonal changes of pregnancy will occur. There are a few things that can indicate a molar pregnancy versus a normal pregnancy:

  • More severe morning sickness
  • Vaginal bleeding
  • Increased enlargement of the uterus
  • Abnormally high hCG
  • Thyrotoxicosis (hCG can mimic TSH and stimulate the thyroid to produce excess T3 and T4)


Ultrasound of the pelvis shows a characteristic “snowstorm appearance” of the pregnancy.

Provisional diagnosis can be made by ultrasound and confirmed with histology of the mole after evacuation.



Management involves evacuation of the uterus to remove the mole. The products of conception need to be sent for histological examination to confirm a molar pregnancy. Patients should be referred to the gestational trophoblastic disease centre for management and follow up. The hCG levels are monitored until they return to normal. Occasionally the mole can metastasise, and the patient may require systemic chemotherapy.


Last updated August 2020