Molar pregnancy is due to an abnormality occurring during fertilization that causes abnormal development of the placenta. There are two types of molar pregnancy:

• complete molar pregnancy (or complete hydatidiform mole) results from fertilization between an anucleated ovum (without a nucleus and therefore without genetic material) and one or two haploid spermatozoa (containing a single copy of each chromosome). The product of this pregnancy does not contain an embryo but only the placenta which develops in the form of multiple cysts (called “grape cluster”).
• partial molar pregnancy (or partial hydatidiform mole) results from fertilization between a normal egg and two spermatozoa or an abnormal sperm. There is an embryo, but it is not viable, and the placenta is developing abnormally.

In both cases the egg does not have complete genetic material, so the pregnancy is doomed to failure.

Molar pregnancy can manifest itself in different forms:

• in its typical form it results in fairly heavy bleeding responsible for anemia and an increase in the volume of the uterus. An increase in the signs of pregnancy or toxemia of pregnancy is sometimes observed. An endovaginal pelvic ultrasound followed by a measurement of total serum hCG will make it possible to make the diagnosis of molar pregnancy.
• in the form of a spontaneous miscarriage. It is then the pathology of the curettage product that will allow the diagnosis of molar pregnancy to be made.
• in asymptomatic form, molar pregnancy will be discovered by chance on ultrasound.

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Complete or incomplete, molar pregnancy is not viable, it is therefore necessary to quickly evacuate the product of the pregnancy. This is done by uterine aspiration performed under ultrasound control. An anatomopathology of the product of pregnancy is usually performed in order to diagnose the type of mole.

An ultrasound check is systematically performed in the 15 days following aspiration in order to verify the absence of retention, a frequent complication of molar pregnancy. In the event of retention, a second aspiration will be performed.

After evacuation of the mole, the level of hCG is closely monitored at the rate of a weekly blood test. This monitoring must be continued after the rate has been negated (i.e. 3 successive negative rates):

• for 6 months in the event of a partial hydatidiform mole;
• for 12 months in case of complete hydatidiform mole;
• for 6 months if, in the case of complete hydatidiform mole, the hCG level becomes negative within 8 weeks (2).

A stagnant or even increasing hCG level suggests a gestational trophoblastic tumor, a complication of molar pregnancy affecting nearly 15% of complete moles and 0,5 to 5% of partial moles (3). It happens that the molar tissue remains in the uterus, proliferates and is transformed into a tumor tissue more or less aggressive and can invade the walls of the uterus and sometimes distant organs. This is called an invasive mole, or choriocarcinoma. A check-up will then be carried out and depending on the results, chemotherapy will be undertaken. Depending on the risk of the tumor (established according to the FIGO 2000 score), the cure rate is estimated between 80 and 100% (4). After the end of treatment, a monitoring period with a monthly dosage of hCG is recommended for 12 to 18 months.

As soon as the follow-up of the mole is finished, it is possible to start a new pregnancy. The risk of having a molar pregnancy again is low: between 0,5 and 1% (5).

In the event of a trophopblastic tumor, treatment with chemotherapy does not affect fertility. Another pregnancy is therefore possible after the end of the monitoring period. However, a dosage of the hCG hormone will be carried out at 3 months of pregnancy and then after pregnancy, two periods at risk of reappearance of the disease.