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Molar pregnancy
Molar Pregnancy
A molar pregnancy or hydatidiform mole is a pregnancy complication that occurs in approximately 1 in 1000 pregnancies. It occurs when there is a problem with fertilization between the egg and the sperm.
Types of molar pregnancy.
Complete mole
In a complete mole the nucleus of the mother’s egg becomes lost or inactivated during fertilization. As a result the fertilized egg has none of the mother’s chromosomes. To compensate the father’s chromosomes are doubled and this prevents an embryo from forming. Abnormal placental tissue then forms and fills the uterus.
Partial mole
In a partial mole, two sperm fertilize one egg. This causes an abnormal embryo to form with 69 chromosomes, instead of 46. Aswell as abnormal placental tissue, there may be some normal placental tissue and membranes with the uterus. The pregnancy is unable to continue.
What causes it?
No definite cause has been identified, but the following may increase the risk of having a molar pregnancy:
• Age > 40 years and < 15 years
• Previous history of molar pregnancy
• Possible ovulatory disorders
• History of miscarriage
• A diet low in carotene (a form of vitamin A)
• Living in certain geograhic locations – e.g. Southeast Asia, Mexico
Complications
In about 20% of complete moles and 2% of partial moles, some of the abnormal tissue persists. Further treatment is then required with drugs such as methotrexate. Rarely it can become cancerous and invade other organs. If left untreated this is extremely dangerous, hence why women diagnosed with molar pregnancies are all followed up closely, see below. However, if treated, usually with a combination of chemotherapeutic drugs, it is usually successful in almost 100% of cases in stopping spread of the disease.
Signs and symptoms
Some women may have no signs and symptoms. The most common symptom is of vaginal bleeding, as most molar pregnancies are now detected early before the onset of more serious signs and symptoms such as:
• Severe nausea and vomiting
• Abdominal pain or cramps
• High blood pressure
• Coughing (sometimes blood)
• Thyrotoxicosis – high levels of thyroid hormone
Diagnosis
Ultrasound Some molar pregnancies will be suspected on ultrasound. Complete moles tend to have a characteristic appearance and the fact that no developing fetus is seen, can allow the diagnosis to be made. The diagnosis of partial moles is more difficult on ultrasound. Sometimes the sonographer may suspect that the placental tissue looks abnormal, but partial moles tend to be initially classified as an empty sac (blighted ovum/anembryonic pregnancy) or delayed miscarriage (missed miscarriage). The diagnosis of partial mole then only being made after histological examination of tissue by a pathologist after surgical evacuation of the uterus (evacuation of retained products of conception - ERPC).
Surgical
The majority of cases are diagnosed after examination of products of conception by a pathologist. In the majority of cases this will be after an ERPC, but may be after tissue has been passed spontaneously or after treatment with misoprostol.
Management
Management involves removing all of the molar tissue from the uterus. In most cases this will involve an ERPC.
Once the diagnosis of a molar pregnancy has been confirmed, all cases in the UK are referred on to regional trophoblastic centres for follow-up. Follow-up involves the monitoring of blood or urine concentrations of the pregnancy hormone hCG until normal. Sometimes levels of hCG do not decline spontaneously, necessitating treatment with drugs such a methotrexate or other types of chemotherapy.
Future pregnancies
It is advisable not to conceive until advised safe by the regional trophoblastic centre. This is usually 6 months after hCG levels have been normal if no additional treatment has been needed. Although there is a risk of having a further molar pregnancy, that risk is low and more than 98% of women who become pregnant after a molar pregnancy will not have a further mole.
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