Hydatidiform mole

Hydatidiform moles are one of the most common but benign forms of gestational trophoblastic disease

It is a common complication of gestation, estimated to occur in one of every 1,000-2,000 pregnancies 3. These moles can occur in a pregnant woman of any age, but the rate of occurrence is higher in pregnant women in their teens or between the ages of 40-50 years. There is a relatively increased prevalence in Asia (for example compared with Europe).

A hydatidiform mole can either be complete or partial. The absence or presence of a fetus or embryo is used to distinguish complete from partial moles:

  • complete moles are associated with the absence of a fetus
  • partial moles usually occur with an abnormal fetus or may even be associated with fetal demise

Rarely, moles co-exist with a normal pregnancy (co-existent molar pregnancy), in which a normal fetus and placenta are seen separate from the molar gestation.

Ninety percent of complete hydatidiform moles have a 46XX diploid chromosomal pattern. All the chromosomes are derived from a single sperm in 90% or less likely two sperms, suggesting fertilization of a single egg that has lost its chromosomes.

With partial moles, the karyotype is usually triploid (69XXY): the result of fertilization of a normal egg by two sperm, one bearing a 23X chromosomal pattern and the other a 23Y chromosomal pattern.

Complete hydatidiform moles usually occupy the uterine cavity and are rarely located in fallopian tubes or ovaries.

The chorionic villi are converted into a mass of clear vesicles that resemble a cluster of grapes.

In the classic case of molar pregnancy, quantitative analysis of beta-HCG shows hormone levels in both blood and urine greatly exceeding those produced in a normal pregnancy at the same stage. 

Please refer to the dedicated articles for discussion on the radiographic features: 

A complete mole can progress to invasive mole (~15%) or to gestational choriocarcinoma (~7%). 

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Article information

rID: 13159
Section: Pathology
Tag: cases
Synonyms or Alternate Spellings:
  • Hydatidiform molar pregnancy

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Cases and figures

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    Case 1: complete mole
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    Case 2: complete mole with bunch of grapes sign
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