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Molar Pregnancy
A molar pregnancy (also known as a hydatidiform mole) occurs when the tissue surrounding a fertilised egg develops abnormally. Its existence normally becomes apparent when a miscarriage occurs.
A dilation and curettage (D & C) is normally performed following miscarriage to remove potentially cancerous molar tissue from the uterus. Approximately 15% of molar pregnancies become cancerous.
A molar pregnancy is a condition in which the tissue surrounding a fertilised egg develops abnormally. This tissue, which would normally have developed into the placenta, instead forms a grapelike mass of tissue inside the uterus.
There are two different types of molar pregnancy:
Partial molar pregnancy
In addition to the abnormal tissue, some normal pregnancy tissue develops eg: a foetus, amniotic tissue or umbilical cord. If a foetus develops, it will die early in the pregnancy as a result of the condition.
Complete molar pregnancy
Where no normal pregnancy tissue develops at all.
Molar pregnancies tend to occur more commonly in younger and older women. In New Zealand it is estimated that 1 in every 1500 pregnancies will be a molar pregnancy. Having a previous molar pregnancy increases the chance of having another molar pregnancy to 1 in 70.
The condition is usually benign (non-cancerous), however molar pregnancies can become cancerous if not removed. The chances of a molar pregnancy becoming cancerous are higher with a complete molar pregnancy than with a partial molar pregnancy.
The cause of molar pregnancy is not fully understood.
Women with a molar pregnancy will have a positive pregnancy test and for the first three to four months there may be no sign that anything is amiss with the pregnancy.
However, signs and symptoms of a molar pregnancy soon appear and can include:
- Faster than usual growth of the uterus
- Vaginal bleeding
- Nausea and vomiting
- Passage of grapelike tissue from the vagina
- Absence of foetal movement or heartbeat
- High blood pressure
- Hyperthyroidism – an overproduction of thyroid hormones which can lead to weight loss and increased appetite.
In most cases, molar pregnancy is discovered when a miscarriage occurs. If a molar pregnancy is suspected it can usually be detected by ultrasound.
Blood and urine tests may be used to detect abnormally high levels of human chorionic gonadotropin (hCG). This is a hormone normally produced during pregnancy but present at much higher levels with molar pregnancy.
It is important that all of the molar pregnancy tissue is removed from the uterus, to eliminate the potential for cancer to develop.
In most cases the molar pregnancy will miscarry spontaneously by the fourth month of pregnancy. A dilatation and curettage (D & C) may be performed a few days after miscarriage to be certain that no molar tissue is left in the uterus.
If the molar pregnancy does not spontaneously miscarry, the woman may be given a medication to trigger the uterus to release the pregnancy. Again this is usually followed by a D & C.
If the molar pregnancy does not miscarry despite medication being given, a procedure called vacuum aspiration may be performed. This procedure is similar to a D & C. During the procedure a general anaesthetic is given, the cervix is opened and the molar pregnancy is removed using a gentle suction instrument. The uterus is then checked to make sure all of the molar tissue has been removed.
For women who are older and do not want any more children, a hysterectomy may be considered, as this eliminates the chance of cancer developing as a result of the molar pregnancy.
Because of the risk of cancer developing, monitoring for several months after the molar pregnancy will be required. Blood tests will be performed every two weeks for the first few weeks to monitor the fall of hCG levels. High levels of hCG after the pregnancy has ended can signal the development of cancer as a result of the molar pregnancy.
Approximately 15% of molar pregnancies become cancerous. This usually takes the form of invasive mole - where the molar tissue invades the wall of the uterus, sometimes causing serious bleeding. In approximately 5% of cases the molar pregnancy can lead to choriocarcinoma - a fast growing cancer. Both conditions are extremely curable but early detection is important.
While the condition is being monitored it is important to avoid pregnancy. This may be for a period of up to one year, though recommendations for each woman will differ.
Auckland District Health Board (2006) Molar Pregnancy. Pamphlet. Early Pregnancy Assessment Unit. Auckland
Turkington, C. A. (2006). Hydatidiform Mole. Gale Encyclopaedia of Medicine, Third Edition. Jacqueline L. Longe, Editor. Farmington Hills, MI. Thomson Gale.
Last Reviewed – 17/10/07
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