Miscarriage is the loss of a pregnancy before it has reached 20 weeks' gestation. Miscarriages often…
What is molar pregnancy?
A molar pregnancy is sometimes also known as a hydatidiform mole. The abnormal placental tissue is usually benign, but in some cases it can develop into more serious forms of gestational trophoblastic disease (GTD), which can include cancer.
Signs and symptoms
A molar pregnancy is usually detected early in a pregnancy. It often ends in a miscarriage and is not able to form a viable pregnancy.
- Vaginal bleeding during the first three months of pregnancy;
- Growth of the uterus that does not correspond to the length of the pregnancy (it may be too large or too small);
- Severe morning sickness, and;
- No foetal heartbeat or movement, although molar pregnancy is almost always detected before this becomes an issue.
In a small number of cases, women with a molar pregnancy can also experience symptoms of:
- Hyperthyroidism, and;
- Pre-eclampsia, although earlier in pregnancy than it usually occurs (the first and early part of the second trimesters).
With a molar pregnancy there are usually symptoms that it is not a normal pregnancy; however, some women may have a miscarriage and not be aware that they have had a molar pregnancy unless the tissue from the miscarriage is tested.
A molar pregnancy occurs because, at conception, the embryo develops with an extra set of chromosomes from the father. Why this occurs is not known.
In a normal embryo, cells contain one set of chromosomes from the mother and one set from the father. In a molar pregnancy, more than one set of chromosomes come from the father, either because the chromosomes from one sperm have been duplicated, or because two separate sperm have fertilised the mother's egg (ovum). A complete molar pregnancy occurs when the egg contains no chromosomes, whereas in a partial molar pregnancy the egg contain the normal 23 chromosomes.
This interferes with the normal development of the embryo. The part of the embryo that would have become the foetus (the developing baby) either does not develop at all, or is abnormal. The foetus is not viable and does not survive beyond the first few months of pregnancy.
The placenta, which also develops from the outer cells of the embryo, grows more quickly than usual and forms an abnormal mass of tissue inside the uterus. It produces the hormone human chorionic gonadotropin (hCG), which causes many of the signs of pregnancy, such as morning sickness and tender breasts.
Complete and partial
Molar pregnancies can be:
- Complete, in which there is only abnormal placental tissue (and no foetus), and;
- Partial, in which there is an abnormal foetus and sometimes some normal placental tissue.
The risk of developing more serious forms of gestational trophoblastic disease is slightly higher with complete molar pregnancies.
Invasive and non-invasive
In some cases, the placental tissue can grow into the wall of the uterus. This is called an invasive mole.
Gestational trophoblastic disease (GTD)
In about 10% of women who have a molar pregnancy, levels of hCG do not return to normal  . This is called persistent gestational trophoblastic disease (GTD). Symptoms can include vaginal bleeding and pain and swelling in the abdomen that continue after the pregnancy.
In rare cases, the abnormal placental tissue can develop over time into cancer.
Forms of cancer that can occur in gestational trophoblastic disease include:
- Placental-site trophoblastic tumour, and;
- Epithelioid trophoblast tumour.
These cancers can occur following normal pregnancies as well as molar pregnancies and can spread to the rest of the body, particularly the lungs, liver and brain.
Women may be at an increased risk of having a molar pregnancy if they:
- Are of Asian background;
- Are under 20 or over 40 years of age, and;
- Have a history of previous gestational trophoblastic disease (including molar pregnancy).
Methods for diagnosis
In some cases, a molar pregnancy will be detected as part of a routine ultrasound during early pregnancy. Your doctor will ask you about your symptoms and your medical history. They may ask questions about any previous pregnancies, births, miscarriages or abortions.
Tests may include:
- A pelvic examination;
- An ultrasound to investigate the uterus, and;
- A blood test to detect levels of human chorionic gonadotropin.
Other tests such as a computerised tomography (CT) scan or magnetic resonance imaging (MRI) may be recommended if other health conditions (including more serious forms of gestational trophoblastic disease) are suspected of causing symptoms.
Types of treatment
In most cases, the main treatment for molar pregnancy is to remove the abnormal placental tissue.
Treatments that may be recommended include:
- Evacuation of the uterine contents, and;
- Hysterectomy (which may be an option for older women who do not want any more children).
In a molar pregnancy, there will often be continued symptoms, such as vaginal bleeding following a miscarriage. Evacuation of the uterine contents may be recommended to ensure that all of the abnormal placental tissue has passed out of the uterus. This can be done using surgery or medication depending on individual circumstances.
If any of the abnormal placental cells remain in the uterus, they can develop into more serious forms of gestational trophoblastic disease. To monitor this, levels of hCG are regularly tested in the weeks and months after the end of the pregnancy, to ensure it returns to normal levels. This may be done by urine or blood tests.
To ensure hCG levels return to normal, you will generally be advised to avoid getting pregnant again for a certain period of time.
Women who have had one molar pregnancy have an increased risk (about one in 100) of having it occur again in a later pregnancy.  To detect any problems early, you may be recommended to have:
- An early ultrasound during any future pregnancies, and;
- A blood test to determine your levels of hCG six weeks after the end of any future pregnancy.
When a pregnancy ends, it can be very distressing and recovering emotionally can take time. Speaking to your doctor or a mental health professional can help. Counselling services may be available at your hospital.
In most cases, treatment of a molar pregnancy by evacuation of the uterus is successful. Most women can have normal pregnancies in the future, although there is about a one in 100 chance of having another molar pregnancy. Having regular check-ups and following your doctor's instructions can help to detect any signs of more serious gestational trophoblastic disease.
While molar pregnancies cannot be prevented, seeking antenatal care once you know you are pregnant can help to detect signs early.