Academic Article, July 2026

Molar Pregnancy and Choriocarcinoma:
What You Need to Know

Panida Mathaveechotikul, MD.
Gynecologic Oncology Unit
Department of Obstetrics and Gynecology, Ramathibodi Hospital

           Molar pregnancy and choriocarcinoma are caused by pregnancy abnormalities. Their incidence rates vary worldwide, with the highest numbers in Asia. In Thailand, reports show that molar pregnancy occurs in about 1 to 2 out of every 1,000 deliveries (1). Since a molar pregnancy can develop into choriocarcinoma, close follow-up care after treatment is highly important. Fortunately, the prognosis of choriocarcinoma is generally very positive.

          Molar pregnancy can be divided into two types based on the number of chromosome sets. The first is a complete molar pregnancy (complete hydatidiform mole, or CHM). It has two sets of chromosomes, which come only from the father. The second is a partial molar pregnancy (partial hydatidiform mole, or PHM). It has three sets of chromosomes, coming from both the father and the mother.

         Patients often experience abnormal vaginal bleeding during pregnancy or a miscarriage. Other signs include a uterus that is larger than expected for the stage of pregnancy. An ultrasound typically shows many multiple small hypoechoic lesions the uterus.

        Differentiating between these two types requires a medical examination and laboratory tests. Correctly identifying the type is crucial because their chances of turning into choriocarcinoma (placental cancer) are very different. A complete molar pregnancy has a 13% to 20% chance of becoming cancerous, while a partial molar pregnancy has only a 0.5% to 5% chance (2).

        Treatment involves a procedure to remove the tissue from the uterus (suction curettage) or surgery to remove the uterus entirely (hysterectomy). A hysterectomy may be considered for those advanced maternal age who already have enough children. In a systematic review and meta-analysis show that patients who have their uterus removed have a statistically significant lower chance of developing cancer (3).

        Monitoring pregnancy hormone (hCG) levels after treatment allows for a quick diagnosis if the condition turns into placental cancer. Patients should have blood tests to check their hCG levels every 1 to 2 weeks until the levels return to normal for 3 consecutive weeks. After that, the follow-up steps depend on the type of molar pregnancy:

• For a partial molar pregnancy (PHM): Patients will have one more follow-up visit, which includes a medical history review, a physical examination, and an hCG blood test 1 month after their hCG levels become normal.

• For a complete molar pregnancy (CHM): Patients must have their hCG levels checked every month for a period of 6 months (4).

         During this follow-up period, patients must use contraception (birth control) to avoid any confusion with a new pregnancy.

         According to The International Federation of Gynecologists and Obstetricians (FIGO) (5), placental cancer after a molar pregnancy (Post-molar GTN) is diagnosed if any of the following criteria are met:

1. hCG levels stay flat (plateau): The hormone levels remain steady or change by no more than 10% for 3 weeks in a row. This is based on blood tests done on days 1, 7, 14, and 21.

2. hCG levels keep rising: The hormone levels increase for 2 weeks in a row. This is based on blood tests done on days 1, 7, and 14.

3. Tissue biopsy results: A tissue sample collected from a uterine curettage is confirmed to be choriocarcinoma.

        The chance of having another molar pregnancy is quite low, at around 1% to 2%. The risk is even lower if the previous one was a partial molar pregnancy (PHM). In rare cases where it happens repeatedly, it often affects members of the same family. This suggests that the condition can be linked to genetics, a condition known as familial recurrent hydatidiform moles (FRHM). It is passed down through families (autosomal recessive) and is caused by abnormalities in specific genes called NLRP7 and KHDC3L (6).

        In conclusion, a molar pregnancy is an abnormal pregnancy that can be successfully treated. The most important key is close monitoring and a quick diagnosis, as there is a chance it can develop into choriocarcinoma (placental cancer). Prompt follow-up ensures fast treatment and reduces the risk of further complications from the disease.

Reference

1. Lertkhachonsuk R, Lertkhachonsuk A. Gestational Trophoblastic Disease. 1st ed. Bangkok: Concept Medicus; 2019.

2. Ngan HYS, Seckl MJ, Berkowitz RS, Xiang Y, Golfier F, Sekharan PK, et al. Diagnosis and management of gestational trophoblastic disease: 2025 update. Int J Gynaecol Obstet. 2025

3. Zhao P, Lu Y, Huang W, Tong B, Lu W. Total hysterectomy versus uterine evacuation for preventing post-molar gestational trophoblastic neoplasia in patients who are at least 40 years old: a systematic review and meta-analysis. BMC Cancer. 2019;19:13

4. Coyle C, Short D, Jackson L, et al. What is the optimal duration of human chorionic gonadotrophin surveillance following evacuation of a molar pregnancy? A retrospective analysis on over 20,000 consecutive patients. Gynecol Oncol. 2018;148(2):254-257.

5. Ngan HYS, Seckl MJ, Berkowitz RS, et al. Diagnosis and management of gestational trophoblastic disease: 2021 update. Int J Gynaecol Obstet. 2021;155(Suppl 1):86-93.

6. Fisher RA, Maher GJ. Genetics of gestational trophoblastic disease. Best Pract Res Clin Obstet Gynaecol. 2021;74:29-41.