Follow-up after treatment for molar pregnancy

Structured follow-up is absolutely essential after a diagnosis of molar pregnancy. Molar pregnancy is a benign condition but with a malignant potential.

The potential for malignancy remains for several months after the evacuation of the uterus. Follow-up is recommended for about one or two years, during which the woman should not try to conceive. Most experts consider one year adequate.

Follow-up normally involves the patient giving urine samples at timed intervals, which may be weekly at first, then fortnightly, monthly and so on. Pregnancy hormone levels in the urine are quantified. These are expected to fall steeply to virtually undetectable levels within weeks of the evacuation. Needless to say, pregnancy, during this follow-up period will complicate the picture.

Monitoring hCG hormone levels during follow-up

Normally, levels of the pregnancy hormone hCG drop steeply and rapidly after the uterine contents have been evacuated. If levels are persistently elevated after the evacuation, it might mean that the patient has what is known as a "persistent mole", an invasive mole or, more seriously, a malignant transformation into what is known as choriocarcinoma.

Tests will be carried out to verify which is which. Treatment in the form of chemotherapy will almost certainly be embarked upon. Success with treatment is excellent, even with choriocarcinoma, provided it is started in time. This is the essence of close follow-up.

Transformation of molar pregnancy into (malignant) choriocarcinoma

Less than 1 in 20 (5%) of molar pregnancies are complicated by malignant transformation. The risk of transformation depends on several factors and is higher among those who have a previous history of molar pregnancy and older mothers (i.e. those above 39 years of age). It is, however, important to stress that all affected mothers need the close follow-up.

Predisposing factors to molar pregnancy

Curiously, this condition is most common in the Far East where, in some countries such as Taiwan, molar pregnancies constitute about 1% of all pregnancies. Compare this with less than 0.05% in western Europe (or 1 in 2000), which means it is more than twenty times commoner in some countries of the Far East compared to western Europe.

Environmental or genetic predisposition to molar pregnancy

There is no compelling evidence that environment factors play a crucial role. If it was environmental, you would expect Caucasians in the Far East to have increased incidence, to match the natives of those countries. This has not happened.

On the other hand, in the USA with a large immigrant community from the Far East, the incidence of molar pregnancy among them appears to be the same as that of other ethnic groups and is nowhere near that seen in their ancestral lands. This makes genetic predisposition unlikely. The important predisposing factors therefore remain elusive.

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