Gestational trophoblastic disease (GTD) is a broad term encompassing both benign and malignant growths arising from products of conception in the uterus.
GTD may be classified as follows:
- Hydatidiform mole (HM).
- Gestational trophoblastic neoplasia.
- Invasive mole.
- Placental-site trophoblastic tumor (very rare).
- Epithelioid trophoblastic tumor (even more rare).
The reported incidence of GTD varies widely worldwide, from a low of 23 per 100,000 pregnancies (Paraguay) to a high of 1,299 per 100,000 pregnancies (Indonesia). However, at least part of this variability is caused by differences in diagnostic criteria and reporting. The reported incidence in the United States is about 110 to 120 per 100,000 pregnancies. The reported incidence of choriocarcinoma, the most aggressive form of GTD, in the United States is about 2 to 7 per 100,000 pregnancies. The U.S. age-standardized (1960 World Population Standard) incidence rate of choriocarcinoma is about 0.18 per 100,000 women between the ages of 15 years and 49 years.
Two factors have consistently been associated with an increased risk of GTD:
- Maternal age.
- Prior history of HM.
If a woman has been previously diagnosed with an HM, she carries a 1% risk of HM in subsequent pregnancies. This increases to approximately 25% with more than one prior HM. The risk associated with maternal age is bimodal, with increased risk both for mothers younger than 20 years and older than 35 years (and particularly for mothers >45 years). Relative risks are in the range of 1.1 to 11 for both the younger and older age ranges compared with ages 20 to 35 years. However, a population-based HM registry study suggests that the age-related patterns of the two major types of HM-complete and partial HM -are distinct. (Refer to the Cellular Classification of Gestational Trophoblastic Disease section of this summary for more information.) In that study, the rate of complete HM was highest in women younger than 20 years and then decreased monotonically with age. However, the rates of partial HM increased for the entire age spectrum, suggesting possible differences in etiology. The association with paternal age is inconsistent. A variety of exposures have been examined, with no clear associations found with tobacco smoking, alcohol consumption, diet, and oral contraceptive use.