Complete hydatidiform mole

Complete hydatidiform mole (CHM) is a type of molar pregnancy and falls at the benign end of the spectrum of gestational trophoblastic disease


CHM is the commonest type of gestational trophoblastic disease.


Complete moles are characterised by the absence of a fetus or fetal parts (i.e. no embryonic tissues). There is a non-invasive, diffuse swelling of chorionic villi.

Chromosomal composition

Approximately 90% of complete hydatidiform moles have a 46XX diploid chromosomal pattern with ~10% having a 46XY composition. All the chromosomes are derived from the sperm, suggesting fertilization of a single egg that has lost its chromosomes.


Serum beta HCG levels are markedly elevated, out of proportion to the pregnancy. 

Radiographic features

  • may be seen as an intrauterine mass with cystic spaces without any associated fetal parts
  • may be difficult to diagnose in the first trimester 6
    • may appear similar to a normal pregnancy or as an empty gestational sac
    • <50% are diagnosed in the first trimester
  • bilateral theca lutein cysts may also be seen on ultrasound

MRI may demonstrate a heterogenous mass with cystic spaces distending the uterine cavity. Fetal parts are notably absent. Uterine zonal anatomy is often distorted although a hypoechoic irregular myometrial boundary may be seen 3.

  • T1: there may be areas of high signal corresponding to foci of haemorrhage
  • T2: there is heterogenous high signal from the cystic spaces
  • T1 C+ (Gd): often demonstrates intense enhancement due to hypervascularity

MRI may also demonstrate bilateral theca lutein cysts.


A complete mole is itself benign, but is considered a pre-malignant lesion. Degeneration into more invasive and malignant types of gestational trophoblastic disease can can occur in ~10-20% of cases.

Treatment and prognosis

Suction and curettage is used for evacuation.

See also

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