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HCG Testing Following a Molar Pregnancy

Author:   Peter Sedesse MD

What is a Molar Pregnancy

A molar pregnancy occurs when sperm fertilizes an egg that contains no genetic material. The egg, with only the male DNA, then implants in the uterus and begins to develop a placenta. Because of the lack of proper DNA, no fetus ever develops and the placenta instead grows like cancer. This will cause bleeding very early in the pregnancy, and the abnormal pregnancy is usually verified at the first ultrasound or by abnormally high HCG test results. This is an emotionally horrible situation for most women as for those first few weeks they believe they are pregnant, only to be told at the ultrasound that there is no pregnancy, only the possibility of cancer.

Initial Treatment for a Molar Pregnancy

Following the ultrasound, a procedure called a D&C is usually performed to remove the abnormal placenta from the uterus and end the molar pregnancy. A baseline HCG test will also be performed at this time. There are two risks following the D&C, first is the chance that not all the placental tissue was removed from the uterus during the D&C, and more serious, the chance that some of the placenta cells had already entered the bloodstream and are now located elsewhere in the body. Both situations are dangerous because these cells have abnormal DNA and will grow in a cancer-like manner no matter where they are located. The most common place for these cells to end up once in the bloodstream is the lungs, but they can end up in many different organs.

HCG hormone levels following a Molar Pregnancy D&C

HCG is a hormone that is secreted by placenta cells and is the hormone that is tested for in pregnancy tests. The presence of HCG in the blood indicates that a placenta is developing, and thus, the woman is pregnant. Because this direct relationship between the presence of HCG and the presence of placenta cells, HCG is an accurate way following a molar pregnancy to determine if there are still placenta cells in the body. If the placenta was effectively removed from the uterus and none of the placenta cells made it into the bloodstream, HCG testing should give a 0 result a few weeks after the D&C.

If the D&C was successful and there are no other placenta cells in the body, it normally takes two to five weeks for HCG hormone levels to reach 0. A baseline HCG test was done usually the same day as the ultrasound, the test results for that day will be very high because the full placenta was still in the body. Sometimes the results will be as high as 100,000 mui/ml. HCG testing must then be done every week for at least a few months. In most cases if the D&C was successful, HCG levels will drop dramatically one week later, usually below 1,000 mui/ml. In the weeks following, the decline will continue rapidly, and should reach below 5 within a few weeks. It is vital that weekly HCG testing is done until the result is under 5, and preferably 0. In the first 6 weeks following a molar pregnancy D&C, HCG testing should always indicate lowering HCG levels. Any increase could indicate not all the placenta tissue was removed from the uterus and has begun to grow.

Limitations of HCG Testing

Because of the limitations of HCG testing, a 0 result does not indicate the complete absence of any placenta cells. While reaching a 0 level is a time for relief, it is important to remember there could still be a few abnormal placenta cells in the body that are not producing enough HCG for the test to reveal. It is for this reason, that even after a 0 result has been reached, it is absolutely vital to continue to have monthly HCG tests performed for at least a year to ensure that the result stays at 0.

Importance of Regular HCG Testing Following a Molar Pregnancy

If HCG testing is done monthly and there are placenta cells located somewhere else in the body, the test result will indicate a rise above 0. This will result in chemotherapy being necessary. The placenta cells are very susceptible to chemotherapy, and if monthly HCG testing is done the cells wouldn´t have had much time to grow, therefore the chemotherapy used is extremely mild and very effective. If HCG testing has not been done monthly, there is a chance the cells could have grown much bigger, and more intensive chemotherapy will need to be used. This is the reason why monthly testing is absolutely needed even after the HCG test results reached 0.

Women who have had a molar pregnancy need to ensure that they do not become pregnant again for at least a year. The reason for this is that a new pregnancy would result in a new placenta, which would produce HCG. This HCG prevents the doctor from being able to tell if HCG is being produced by other placenta cells somewhere else in the body.

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