6: Gestational Trophoblastic Disease

Gestational trophoblastic disease is uncommon (about 1/1000 pregnancies). There are several forms:

  • Molar pregnancy (complete, partial)
  • Persistent gestational trophoblastic neoplasia
  • Gestational choriocarcinoma (as opposed to non-gestational choriocarcioma which is a germ cell tumour)
  • Placental Site trophoblastic tumour

Hydatiform Mole


Hydatiform mole occur in about 1/1000 pregnancies. Of these, about 2/3rds are partial moles and 1/3rd are **complete moles. The are more common in older, fertile women.


Complete moles arise from fertilisation of an empty ovum:

  • Most cases (80%) arise from fertilisation by a single 23X sperm which duplicates its haploid genome, forming a 46XX genome.
  • A minority of cases arise from fertilisation of an empty ovum by two sperm (23X + 23X or 23X + 23Y)
  • 46YY is not viable and does not develop into anything

Partial moles arise from fertilisation of a normal ovum by two sperm, leading to 69XXY, 69XXX or 69XYY.
It appears that presence of the Y chromosome in a complete mole is associated with increased risk of persistent and transformed disease.

Why does a mole develop?

The paternal component of the genome is mostly responsible for growth of the placental tissues; therefore presence of two paternal genomes causes abnormal overgrowth of the placenta.

Natural History

Most molar pregnancies are detected at the 12 week ultrasound, or earlier due to hyperemesis.

Tumour Features

Complete Mole

In a complete mole there is no fetal tissue. The macroscopic appearance is of multiple villi with central cavitation, giving a 'grape like' appearance. Microscopically, there is central necrosis within atypical trophoblast.

Partial Mole

Partial moles contain both abnormal and normal chorionic villi.

Gestational Choriocarcinoma

This has a similar appearance to non-gestational choriocarcinoma. The risk is highest after a complete mole, but it can occur after a normal pregnancy (1:150,000).


Staging is with TNM and FIGO, which match.

T Stage

  • T1: Confined to uterus
  • T2: Invades pelvic structures

M Stage

  • M1a: Lung metastases
  • M1b: Other metastases

Final Stage

Stage T M
I T1 M0
II T2 M0
III Tany M1a
IV Tany M1b