A molar pregnancy is a rare abnormality that occurs in pregnancy. During the fertilization process, certain abnormalities in the cells grow to form the placenta. A molar pregnancy is also referred to as a "hydatidiform mole" because it can be associated with conditions called gestational trophoblastic tumours. These are generally curable, benign tumours that can spread outside of the uterus (1).
How Molar Pregnancy Develops
Normal pregnancies should involve all 23 chromosomes each from the mother and the father. In a molar pregnancy, the father's 23 chromosomes are doubled. The mother's 23 chromosomes will either be present or not. A mass of tissue, commonly referred to as a "cluster of grapes," will result (2).
Molar pregnancies can be classified into two categories:
Complete Molar Pregnancy
In this case, the egg will have a duplicate number of paternal chromosomes (therefore, 46 in total from the father), but no maternal chromosomes. If this happens, no embryo will develop, and neither the amniotic sac nor regular placental tissue will form. A mass of cysts will form instead (2).
Partial Molar Pregnancy
A molar pregnancy will be considered "partial" if the egg has double the amount of chromosomes from the father (therefore, 46 in total from the father), and the mother's usual 23 chromosomes. Thus, the egg will end up with 69 chromosomes in total. If this occurs, the embryo will start to develop, but is abnormal and will never grow into a healthy, full-term baby (1).
Thankfully, these pregnancies are rare. They occur in approximately 1/1000 pregnancies in North America and the UK. For some unknown reason, Asian women are three times more likely to develop a molar pregnancy (1).
Signs And Symptoms Of A Molar Pregnancy
Typical signs of a molar pregnancy include (1):
- vaginal bleeding, beginning anywhere from 6 to 16 weeks
- nausea and/or vomiting
- abdominal swelling
- unusually high hcg levels
- mass of cells shown on an ultrasound
Treatment
If a molar pregnancy is detected, there are two possible methods of treating it. A medication can be administered to initiate a miscarriage of the abnormal tissue. A D&C (short for "dilation and curettage") may be performed, which is a surgery involving the removal of the abnormal tissue. This type of surgery is done in other types of miscarriages where the pregnancy tissue does not miscarry on its own (1).
A woman who suffers from a molar pregnancy must be monitored by a doctor on a regular basis for about six months to a year afterwards to ensure that the mole does not grow back. Hcg levels in the blood will be monitored to make sure that they decrease and return to a non-pregnant state.
Sometimes the molar tissue can grow into the muscle layer of the uterus. This can be dangerous as this abnormal tissue can travel through the blood to vital organs.
In approximately 15% of complete molar pregnancies, and in less than 1% of partial molar pregnancies, certain abnormal cells can still remain after treatment. This is referred to as "persistent gestational trophoblastic disease," which will require chemotherapy to remove all the abnormal tissue. Treatment will continue until the hcg levels have returned to normal (1).
There is a very small chance that a complete molar pregnancy can lead to rare form of cancer called "choriocarcinoma," which is curable. This happens when the placenta becomes malignant.
Although molar pregnancies can be dangerous, they are absolutely curable. In fact, almost 100% of molar pregnancies are curable if they haven't spread beyond the uterus. If they have spread to other organs, the disease is still curable in most cases. Once the body is completely free of the abnormal tissue, hcg levels will most likely have to be monitored for a very long time after a cancer has developed (1).
When Subsequent Pregnancies Can Occur
Generally, it is advised that women wait about six months before trying to get pregnant again after a molar pregnancy has been cured. If chemotherapy was involved, this wait should be extended to 12 months. This is mainly because the doctors would like to be sure that the rise in hcg levels is not from a recurrence of a mole rather than a normal pregnancy (1).
A molar pregnancy is devastating, as is any form of miscarriage. It is important to talk to someone if feelings of sadness are impeding on the quality of life. Fortunately, a molar pregnancy should not have any influence on a woman's ability to get pregnant again.
For more pregnancy-related information, please visit: www.complete-pregnancy-guide.com
References:
1. Eisenberg et al, What to Expect When You're Expecting, 1991
2. healthlinkbc.ca
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