How is a molar pregnancy diagnosed? What exactly is a partial molar? I had a miscarriage, and while I was pregnant I was taking progesterone. There was a heartbeat. My pathology report came back saying there were possible signs of a molar pregnancy. The report cited high levels of hCG. If my baby had died before the physical signs of a miscarriage and I continued the progesterone pills, could the degeneration and pills account for the high hCG levels? What other signs would indicate a molar pregnancy?

-- Kim

A molar pregnancy is the result of egg fertilization where only the sperm chromosomes develop. The sections of the placenta become bloated with fluid and take on an appearance similar to a bunch of grapes. This is most often diagnosed by an atypically enlarged uterus, high hCG level or appearance on ultrasound. Because there is no fetus in a molar pregnancy, there is no heartbeat.

A partial mole is seen less frequently. In this condition, there is both a molar pregnancy and a fetus; there may or may not be a heartbeat. This condition is diagnosed at the time of miscarriage or ectopic pregnancy.

After a complete evaluation shows the presence of a molar pregnancy, your physician will perform a suction dilation and curettage (D&C). It is important to keep testing your hCG levels to make sure they drop back to zero. That's because molar tissue may occasionally remain after D&C, and in rare cases it can progress to a precancerous or cancerous state. These conditions are called gestational trophoblastic disease (GTD). Luckily, with careful monitoring and rapid treatment, GTD can be successfully eliminated before a cancer develops. In order to be sure no further molar tissue remains, you will be asked to avoid pregnancy for at least one year after the D&C.

But quite often -- and what seems to be the case for you -- a molar pregnancy is not diagnosed before the D&C. Instead, while reviewing the pathology slides, the physician sees swelling of the placental sections and determines that molar degeneration is present.

Molar degeneration is not the same thing as molar pregnancy. The criteria for molar pregnancy includes swelling of the placenta, missing blood vessels and an overgrowth of placental cells. This condition warrants the precautions listed above. In contrast, molar degeneration is a condition marked by the same type of placental swelling, but not the blood vessel development and the overgrowth of placental cells seen in a molar pregnancy. Molar degeneration is likely an artifact of miscarriage, which means the pregnancy may or may not have a heartbeat.

When a diagnosis of molar degeneration is made, your risk of cancer or recurrence is quite low. In fact, while molar degeneration may look similar to GTD under the microscope at first glance, it is likely totally unrelated to the more concerning conditions of molar pregnancy or partial mole, and of no real significance.