What is a molar pregnancy?
A molar pregnancy, sometimes called a hydatidiform mole or gestational trophoblastic disease, is a rare complication of pregnancy, which results from a problem related to the genetic makeup of the fused egg and sperm and which occurs during conception. This causes a fluid-filled mass of tissue to grow inside the womb, instead of a healthy pregnancy. A molar pregnancy will not develop into a baby.
A molar pregnancy will often have the same symptoms as a normal pregnancy in its early stages, and may go undetected until the first routine ultrasound scan, if it is not miscarried before this time. Most molar pregnancies are diagnosed in the first trimester, before any classic signs and symptoms are present. However, symptoms which could indicate a molar pregnancy include vaginal bleeding, severe nausea and vomiting, tummy growth which can be faster or slower than normal, and signs and symptoms of hyperthyroidism.
A molar pregnancy can be removed, and most people will make a full recovery. Very rarely, molar pregnancy may become cancerous. However, these cancers have a very good prognosis with a high cure rate of nearly 100 percent.
Molar pregnancy affects about one in every 1000 or 2000 pregnant people. The reported incidence varies widely in different regions of the world.
Many people experience emotional distress after having a molar pregnancy, particularly if it occurs during a planned pregnancy or if chemotherapy is necessary. A range of therapeutic treatment options are available.
Molar pregnancy symptoms
Molar pregnancy often has no symptoms differing from a normal pregnancy and is frequently diagnosed during a routine ultrasound. However, the most common signs and symptoms that could indicate molar pregnancy are:
- Vaginal bleeding early in the pregnancy, which may contain little fluid-filled cysts
- High level of human chorionic gonadotropin (hCG) (pregnancy hormone)
- Bigger abdomen (tummy) than expected for the number of weeks pregnant
- Pelvic pressure or pain
Less common signs and symptoms include:
- Hyperemesis gravidarum (severe nausea and vomiting)
- Early onset preeclampsia (high blood pressure in pregnancy)
- Signs of hyperthyroidism (overactive thyroid), such as nervousness, insomnia and heart palpitations
Molar pregnancy causes
A molar pregnancy occurs when there is a problem with the genetic information of a fused ovum (egg) and sperm. While a molar pregnancy cannot be predicted, because little is known about how and why it occurs, factors that are thought to increase the risk of having one include:
- Being younger than 15 or older than 35
- A history of molar pregnancy
- A history of miscarriage
- A diet low in carotene (a form of vitamin A)
Types of molar pregnancy
A molar pregnancy may be complete or incomplete, depending on the number of chromosomes of the fertilized egg.
In normal conception, a single sperm with 23 chromosomes fertilizes an egg with 23 chromosomes, making 46 in all.
Complete molar pregnancy
In this situation, one sperm, or sometimes two, fertilize an egg that has no genetic material. No embryo will grow, because there are no maternal chromosomes.
Normally a fertilized empty egg dies, but in rare cases it implants in the uterine wall. This causes trophoblast cells, the cells that would become a placenta, to grow rapidly into clusters of cysts or a complete mole.
Partial molar pregnancy
A partial mole occurs when two sperm fertilize the egg instead of one. This means that there are 69 instead of 46 chromosomes, creating too much genetic material.
Molar pregnancy complications
In some cases, after removal of a molar pregnancy, a number of cells may remain behind and develop into gestational trophoblastic neoplasia (GTN), which is cancerous and can be very serious if left untreated. However, GTN has a very good prognosis, with a near 100 percent cure rate. There are two types of GTN that can result from a molar pregnancy:
Persistent trophoblastic disease (PTD): Also known as an invasive mole or chorioadenoma destruens, PTD is where part of the mole remains in the body and can grow quickly into a locally invasive tumor. This is more likely to occur after a complete molar pregnancy.
Choriocarcinoma: A very rare cancer which grows from the placenta and can metastasize (spread) throughout the body if left untreated. It can also occur after a healthy pregnancy or a miscarriage, but those with a molar pregnancy are at a higher risk.
Molar pregnancy diagnosis
Molar pregnancies are commonly discovered during the first routine ultrasound scan of a pregnancy. If a person develops bleeding in early pregnancy, the doctor will normally arrange a scan, in which case the condition may be found sooner.
The image from the ultrasound scan may be characteristic of a molar pregnancy, showing cysts that resemble a cluster of grapes, in which case the condition will be treated.
Often, however, the image may resemble that of a miscarriage. The further along the molar pregnancy is, the more characteristic the ultrasound picture becomes. If the doctor suspects a molar pregnancy, a blood test will be ordered to check if the hCG levels are higher than normal, far higher in comparison to possible hCG levels that may occur in normal pregnancies. See these resources for more information on miscarriage and signs of miscarriage.
If there is both an ultrasound image that looks like a miscarriage and higher-than-normal hCG levels, the person will be treated to remove the abnormal tissue in the uterus.
Tissue miscarried or removed from the uterus will be sent to a laboratory and tested to see if molar tissue is present. Diagnosis can then be confirmed.
Malignant trophoblastic tumors primarily metastasize to the lungs, so once diagnosis of a molar pregnancy is confirmed, this should be ruled out by taking a baseline chest radiograph.
There may be a delay of a few days or weeks between treatment and the receipt of confirmation that the person had a molar pregnancy.
Molar pregnancy treatment
Treatment for a molar pregnancy usually takes the form of dilation and curettage (D&C), sometimes known as surgical uterine evacuation, dilation and evacuation, surgical management of miscarriage (SMM), evacuation of retained products of conception (ERPC) or a scrape. This is a minor operation done under general anesthetic, in which the cervix, the passage leading from the uterus to the vagina, is dilated so that abnormal tissue in the uterus can be removed with suction and a spoon-like instrument (curette). There is likely to be vaginal bleeding for up to six weeks after surgery, which may be heavy at first.
People who have completed childbearing may have the option of hysterectomy, a surgical procedure to remove the womb.
Molar pregnancy follow-up
There is a small risk of developing gestational trophoblastic neoplasia (GTN) after a molar pregnancy has been treated. GTN is a serious condition that requires rapid treatment, so all people who have had molar pregnancies should be monitored afterwards.
During a molar pregnancy, hCG (pregnancy hormone) levels rise, but should return to normal once the person has been treated. For at least six months after the end of treatment for a molar pregnancy, hCG levels will typically be monitored through urine tests. If they do not return to normal, this could indicate GTN.
It is important to take steps to avoid becoming pregnant for about six months after treatment, as this would interfere with the monitoring of hCG levels for signs of GTN.
After a complete mole, the likelihood of developing GTN is significantly increased. After a partial mole, this risk only increases slightly. The reported incidence of gestational trophoblastic neoplasia (GTN) after each type of molar pregnancy is:
- Complete mole: 15-20 percent
- Partial mole: 1-5 percent
Molar pregnancy and emotions
It is normal to feel distressed after a molar pregnancy, and in some people these emotions can develop into depression and anxiety if left untreated.
The Miscarriage Association suggests that a person with molar pregnancy might experience a variety of associated feelings, including:
- Shock and confusion. These emotions are especially common if the pregnancy was planned and thought to be healthy prior to an ultrasound scan or miscarriage. It can be shocking for a person to find out they have a condition which they probably never heard of before.
- Fear and anxiety. A molar pregnancy may lead to fear of the possibility of having cancer, and fear that problems will happen again with any future pregnancies.
- Loss and grief. It is normal to feel grief if a baby was expected.
- Feeling stuck. It is common to feel stuck if wanting to try to conceive again and having to wait some time while having follow-up and repeated blood and urine tests.
Counseling is available for people affected by a molar pregnancy. Support groups such as MyMolarPregnancy.com are also available and may be able to put a person in touch with others in a similar situation.
Health practitioners will be able to provide advice to those affected by a molar pregnancy on choosing the most appropriate kind of support and direct them towards available services.
Molar pregnancy FAQs
Q: Can a molar pregnancy survive?
A: No, a molar pregnancy cannot develop into a baby, as it does not have a correct set of chromosomes. Molar pregnancies may at first seem to have the same symptoms as a normal pregnancy and generate a positive result on a pregnancy test. In the case of complete molar pregnancy, no fetus will develop. In a partial molar pregnancy, fetal tissue may initially develop, it will, however, be genetically abnormal and cannot survive, and will be overtaken by rapidly-growing cysts.
Q: Will a person who has had a molar pregnancy be able to have a normal pregnancy in future?
A: Yes, a person who has had a molar pregnancy will normally have no complications with future pregnancies. The risk of another molar pregnancy is increased, but is still only around 1-2 percent. The recurrence rate after two molar pregnancies has been reported to range from 11 to 25 percent. However, a person should take measures to avoid becoming pregnant for at least six months after the end of molar pregnancy treatment, to allow hCG monitoring for remaining molar tissue. If chemotherapy follow-up treatment has been used, a person should take measures to avoid becoming pregnant for at least one year after the end of treatment, to allow for hCG monitoring and also to allow the chemotherapy, which can be very damaging to an unborn baby, to clear the body.
Q: Blighted ovum vs molar pregnancy - what is the difference?
A: Blighted ovum, also known as anembryonic pregnancy, is a condition in which a fertilized egg attaches itself to the uterine wall, but an embryo does not develop, usually due to chromosomal abnormalities or abnormal cell division. Molar pregnancy is caused by chromosomal abnormalities due to abnormal conception, and causes a mass of fluid-filled cysts to grow, instead of a healthy pregnancy. Blighted ovum and partial molar pregnancy can look similar on an ultrasound. However, a partial mole usually shows the remains of embryonic tissue, which never appears in a blighted ovum.
Other names for molar pregnancy
- Hydatidiform mole
- Complete mole
- Partial mole
Patient."Hydatidiform Mole. Molar pregnancy information and causes." 1 Nov. 2016. Accessed 18 April 2018. ↩ ↩
Uptodate. "Hydatidiform mole: Epidemiology, clinical features, and diagnosis" 14 April 2017. Accessed 25 May 2018. ↩ ↩
Hindawi. "Gestational Trophoblastic Disease: A Multimodality Imaging Approach with Impact on Diagnosis and Management." 28 June 2014. Accessed 25 April 2018. ↩