Molar Pregnancy

What is Molar Pregnancy?

Molar pregnancy or hydatidiform mole follows abnormal conception resulting in early loss of pregnancy. It occurs due to a problem at the time of conception, when the egg and sperm fuse. Following conception, the resulting mass of cells (trophoblasts) proliferate but are unable to develop into normal fetus or placenta during pregnancy.

Hydatidiform mole is included under a group of disorders collectively referred to as gestational trophoblastic disease (GTD). Hydatidiform mole per se is a benign condition; however, there is a slight risk that a molar pregnancy can become a cancerous form of GTD called gestational trophoblastic neoplasia (GTN). Cancerous forms include invasive mole and choriocarcinoma.

Fortunately, the occurrence of molar pregnancy is rare.In North America and Europe, the incidence is approximately 60 to 120 per 100,000 pregnancies. The frequency has been found to be higher in other countries of the world such as South Asia.

Normal Pregnancy Overview

Pregnancy results when the egg is fertilized by the sperm. During fertilization (fusion of egg and sperm), genes from the sperm mix with those from the egg to produce the unique features of the baby to be. The fertilization process usually occurs in the tube, and before the fertilized egg reaches the uterus to be implanted, it divides into two main groups of cells as described.

One group of cells called trophoblasts gives rise to the placenta (afterbirth) that nourishes the baby and the membranes that surround the fetus. The other cells form the embryo and develop into the full-grown baby in about 40 weeks.

Many pregnancies are lost even before implantation in the uterus takes place or within the first 12 weeks following implantation. These are also called miscarriages. Molar pregnancy is a type of early pregnancy loss.

What are the Causes of Molar Pregnancy?

A molar pregnancy is caused by an abnormality during conception.

All human cells normally contain 23 pairs of chromosomes. One chromosome in each pair is derived from the father, the other from the mother. In contrast, the reproductive cells namely the sperm and the ovum contain 23 chromosomes each so that the resulting fused cell will contain the normal 23 pairs (46) chromosomes of the human cell restoring the normal number.

Depending on the type of abnormality, molar pregnancy can be classified as a partial or complete mole.

• In a complete molar pregnancy, an empty egg (having no chromosomes) is fertilized by either one or two sperm, and therefore all the genetic material is derived from the father. Normally this fertilized but empty ovum will die. However, rarely, implantation occurs, and the trophoblast cells grow abnormally resulting in a mass of cells with no embryo at all.
• A partial hydatidiform mole can also occur due to abnormal conception. It occurs when two sperm fertilize one normal ovum (which should not usually occur). This means that there is too much genetic material (69 chromosomes) present as also excess trophoblastic tissue. This trophoblast tissue proliferates and overtakes the growth of fetal tissue and no baby forms.

Both partial and complete hydatidiform moles will not produce a live healthy fetus and are 'non-viable' pregnancies. A pregnancy that results in the formation of a hydatidiform mole is referred to as a molar pregnancy.

What are the Risk Factors of Molar Pregnancy?

Certain risk factors are associated with an increased probability of forming a molar pregnancy. These include

• Extremes of maternal age
• More than 35 years carries up to a ten-fold increased risk
• Early teenage pregnancy, usually less than 20 years
• Previous history of molar pregnancy
• History of previous spontaneous miscarriage or infertility
• Dietary factors, eg, diet deficient in beta-carotene and animal fat
• Smoking

What are the Signs and Symptoms of Molar Pregnancy?

A molar pregnancy may seem like a normal pregnancy at first with a positive pregnancy test.

However, the appearance of these symptoms warrants medical attention to rule out something more serious including a molar pregnancy.

• Dark brown to bright red vaginal bleeding during the initial three months (most common symptom)
• Passing grape-like clusters from the vagina
• Absence of fetal heartbeat
• Abdomen feels larger
• Severe nausea and vomiting (excessive morning sickness)
• Pelvic pain and discomfort

Associated (not diagnostic) conditions that may be found by the doctor include

• Uterus unusually large for the stage of pregnancy
• High blood pressure
• Overactive thyroid gland (hyperthyroidism)
• Anemia
• Presence of ovarian cysts

How do you Diagnose Molar Pregnancy?

Most complete moles can be diagnosed on ultrasound scan in early pregnancy. Partial moles are more difficult to diagnose and may be incorrectly classified as miscarriages initially, and diagnosis is made only after pathological examination of the remaining tissue following the evacuation of the products of conception.

Ultrasound Scan

An ultrasound scan is usually done during early pregnancy as a routine. The uterus is imaged using a probe placed on the abdomen that directs high-frequency sound waves at the abdominal and pelvic organs.

An ultrasound of a complete molar pregnancy can be correctly detected as early as 8 to 9 weeks. The findings include

• Absence of embryo or fetus
• Thick placenta nearly filling the uterus
• No amniotic fluid
• Presence of ovarian cysts

An ultrasound of a partial molar pregnancy may show:

• Low amniotic fluid
• A thick cystic placenta
• Fetus showing growth retardation

Serum human chorionic gonadotropin (hCG) levels:

HCG is the pregnancy hormone and is elevated even during normal pregnancy. However, serum levels of hCG will be markedly elevated in molar pregnancy and can help with diagnosis.

How do you Treat Molar Pregnancy?

As mentioned previously, molar pregnancy is a non-viable pregnancy and must be terminated to prevent further complications (small risk of developing cancer). Treatment options include the following.

Dilation and curettage (D&C)

During the procedure, performed under regional or general anesthetic an internal examination is done, and the cervix is visualized and dilated. The contents of the uterus are then removed using suction to evacuate the retained products of conception.

It is usually done as an outpatient procedure, and the removed material is sent off for pathological examination.

Hysterectomy

In women who do not wish to have any more children hysterectomy (removal of the uterus) operation may be preferred to avoid the potentially small risk of cancer in future.

HCG monitoring and Follow-up

After removing the mole, measurements of your HCG level will be regularly done until it returns to baseline for at least six months to ensure there is no molar tissue left. If levels remain, elevated additional treatment may be required.

References:

1. Molar pregnancy - (http://brochures.mater.org.au/brochures/mater-mothers-hospital/molar-pregnancy)
2. Hydatidiform Mole - (https://www.ncbi.nlm.nih.gov/books/NBK459155/)

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