Molar Pregnancy

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What is a molar pregnancy?

A molar pregnancy is a mass of tissue (hydatidiform mole) that forms an abnormal placenta inside the uterus. It starts from two or three sets of the father's chromosomes, with none from the mother.¹ Even though it is not an embryo, a mole triggers symptoms of pregnancy. About 1 out of 1,000 women with early pregnancy symptoms has a molar pregnancy.²

There are two types of molar pregnancy: complete and partial.

• Complete molar pregnancy. In place of a normal placenta and embryo, the hydatidiform mole is abnormal placental tissue that grows into a grapelike cluster that can fill the uterus.
• Partial molar pregnancy. The placenta grows abnormally into molar tissue. Any fetal tissue that develops is likely to have severe defects.

In extremely rare cases, an apparent twin pregnancy is found to be one complete mole and one normal, healthy placenta and fetus.³

What kind of risks are related to a molar pregnancy?

A hydatidiform mole can cause heavy bleeding from the uterus.

Some molar pregnancies lead to abnormal cell growth called gestational trophoblastic disease.

• About 15% to 20% of complete molar pregnancies develop trophoblastic disease that keeps growing after the molar pregnancy is removed. A small percentage of these may become invasive cancer.^{4, 5} Fortunately, nearly 100% of those women who develop cancer are cured with treatment.²
• About 5% of partial molar pregnancies develop trophoblastic disease.⁵

In rare cases, the abnormal tissue can spread (metastasize) to other parts of the body.

What causes a molar pregnancy?

Molar pregnancy is thought to be caused by a problem with the genetic information of an egg or sperm. A molar pregnancy can develop during the earliest stage of a pregnancy when:

• An abnormal egg with no genetic information is fertilized by a sperm. The sperm's chromosomes duplicate and develop into a complete mole.
• A normal egg is fertilized by two sperm. This cell mass is most likely to develop into a partial mole.

Factors that may increase your risk of having a molar pregnancy include:

• Age. Risk for complete molar pregnancy steadily increases after age 35.¹
• History of molar pregnancy, particularly if you've had two or more.⁵
• History of miscarriage.
• A diet low in carotene (a form of vitamin A). Women with low carotene or vitamin A intake have a higher rate of complete molar pregnancy.¹

What are common symptoms of a molar pregnancy?

A molar pregnancy triggers the same first-trimester symptoms that a normal pregnancy does (a missed menstrual period, breast tenderness, fatigue, increased urination, morning sickness). It may be diagnosed during an early ultrasound test. In addition to normal pregnancy signs, a molar pregnancy usually causes additional symptoms, which can include:

• Vaginal discharge of tissue that is shaped like grapes. This is the most characteristic symptom of a molar pregnancy.
• Vaginal bleeding (light or heavy).
• A uterus that is abnormally large for the length of the pregnancy.
• Severe nausea and vomiting.
• Signs of hyperthyroidism, such as fatigue, weight loss, increased heart rate, heat intolerance, sweating, irritability, anxiety, muscle weakness, and thyroid enlargement.
• Pelvic discomfort.

Most of these symptoms can develop along with other conditions, such as a multiple pregnancy, a miscarriage, or even a healthy pregnancy.

How is a molar pregnancy diagnosed?

If you have symptoms that suggest a molar pregnancy, your health professional will do some simple tests. A pelvic exam, a blood test of your pregnancy hormone (human chorionic gonadotropin, or hCG) levels, and a pelvic ultrasound can confirm whether you have a molar pregnancy.

Molar pregnancy may also be found during a routine ultrasound in early pregnancy. Partial molar pregnancies are often found at the time of treatment for an incomplete miscarriage.

How is a molar pregnancy treated?

If you are diagnosed with a molar pregnancy, you will need immediate treatment to remove all molar growth from your uterus. After your uterus is cleared of molar tissue, you will have periodic hCG blood tests to screen for signs of persistent cell growth (trophoblastic disease) in your uterus. These tests are done periodically for 6 to 12 months.

Some women with a molar pregnancy also have a large ovarian cyst (not cancerous).

In some cases, trophoblastic disease can develop into trophoblastic cancer. But most cases are identified early, located in the uterus only, and are highly curable with chemotherapy. In the rare case when cancer has had time to spread to another part of the body, more aggressive chemotherapy is necessary, sometimes combined with radiation treatment.

Most women who have been treated for trophoblastic disease are still able to become pregnant.¹

After having a molar pregnancy, it is common to feel grief over losing a pregnancy and to be fearful about cancer risk. Consider contacting a support group or talking to friends, a counselor, or a religious advisor to help you and your family deal with this difficult time.

Frequently Asked Questions

A molar pregnancy typically triggers common signs of pregnancy—a missed menstrual period, breast tenderness, fatigue, increased urination, and morning sickness.

Contact your health professional immediately if you have signs of pregnancy and develop any of the following during your first trimester:

• Vaginal discharge of tissue that is shaped like grapes. This is the most characteristic symptom of a molar pregnancy.
• Vaginal bleeding (light or heavy). Light vaginal bleeding in the first trimester is common in a normal pregnancy. But it may signal a molar pregnancy or a miscarriage.
• Severe nausea and vomiting. These symptoms occur occasionally in a molar pregnancy.
• Signs of hyperthyroidism, such as fatigue, weight loss, increased heart rate, heat intolerance, sweating, irritability, anxiety, muscle weakness, and thyroid enlargement.

Signs of a molar pregnancy that your health professional might find during an exam include:

• High blood pressure, which is a common symptom of preeclampsia. A molar pregnancy can cause preeclampsia to develop during the first or early second trimester.
• No fetal heartbeat. No fetus is present in complete molar pregnancies and in some partial molar pregnancies.
• A uterus that is abnormally large for the length of the pregnancy. There are reasons other than a molar pregnancy for a large uterus, such as being pregnant with twins or not knowing how long you have been pregnant. But an abnormally large uterus is a common sign of molar pregnancy.

Complete molar pregnancies are now often diagnosed by ultrasound earlier in pregnancy than they were in the past. So, women with complete molar pregnancies seldom have the condition long enough to develop symptoms such as excessive uterine size, nausea, vomiting, preeclampsia, and hyperthyroidism.

Most molar pregnancies are identified when they are still small. If you have symptoms that suggest a molar pregnancy, see your health professional immediately. You will be evaluated with a simple exam and tests, including:

• A pelvic exam, to evaluate the size of the uterus and check for abnormalities.
• A blood test to measure the amount of a pregnancy hormone, called human chorionic gonadotropin (hCG), to see whether the level is abnormally high for the length of the pregnancy.
• A pelvic ultrasound test. If a pelvic exam or hCG level suggests a molar pregnancy, an ultrasound can be used to confirm the diagnosis. Some molar pregnancies are first diagnosed during an ultrasound done for another purpose.

If you are diagnosed with a molar pregnancy, additional blood and urine tests and chest X-ray may be done to check for:

• Preeclampsia.
• Anemia.
• Signs of cancerous tissue.
• Hyperthyroidism caused by the molar pregnancy.

A molar pregnancy is removed with vacuum aspiration under general anesthesia. Pelvic ultrasound may be used during the procedure to guide removal of all the abnormal tissue. Medication (oxytocin) is used during or after the procedure to make the uterus contract—uterine contractions help the uterus shrink to its prepregnancy size and help stop uterine bleeding after the mole is removed.

If you have Rh-negative blood, you will also have a shot of Rh immune globulin. This prevents a problem called Rh sensitization, which can cause serious problems in a future pregnancy.

If you have no future plans to become pregnant, you may consider a hysterectomy, which reduces the chance of developing gestational trophoblastic disease after a molar pregnancy.

If you are considered high risk for developing cancer after a molar pregnancy, you may be treated with methotrexate to prevent persistent cell growth.

In the very rare case that a normal fetus is present along with a mole, the fetus is monitored closely and delivered as soon as possible.

Important follow-up care

If you have had a molar pregnancy, it is important to see your health professional for regular follow-up visits to watch for any cancerous cell growth. Follow-up measures include:

• Measuring hCG levels every 1 to 2 weeks until they are normal, then measuring them every 1 to 2 months for 6 months to a year. Levels of hCG that stay high may be a sign of cancer.
• Preventing pregnancy while hCG levels are being monitored, usually about 6 months. It is very important that you practice highly effective birth control during the entire period of follow-up. For more information on contraception, see the topic Birth Control.
• Close medical supervision if you happen to conceive within 12 months of molar pregnancy treatment.

An obstetrician, a gynecologist, or a doctor specializing in reproductive cancer (gynecologic oncologist) can treat a molar pregnancy.

If you are diagnosed with trophoblastic cancer

Most cases of trophoblastic cancer are confined to the uterus. If you are diagnosed with this low-risk and highly curable type of cancer, you will probably receive one or more series of a medicine—either methotrexate or actinomycin D.

If you are diagnosed with cancer that has spread to other parts of the body, you will probably be treated with a combination of chemotherapy medicines.

Fertility and coping after a molar pregnancy

After a molar pregnancy, your chances of having a successful pregnancy are about the same as those of the general population of childbearing women, even if you have been treated for trophoblastic disease.⁶ But you do have an increased risk for having another molar pregnancy. So, your health professional will want to monitor you closely during and after any future pregnancies. Pregnancy care will include:

• Routine prenatal care and a late first-trimester fetal ultrasound to confirm a healthy pregnancy.
• Checking hCG levels 6 weeks after childbirth to confirm that no trophoblastic disease has developed.

Having a molar pregnancy can challenge your emotional and physical well-being. Grief about losing a pregnancy, combined with fear of cancer, may feel like more than you can handle. Consider contacting a support group or talking to friends, a counselor, or a member of the clergy to help you and your family deal with this difficult time. For more information, see the topic Grief and Grieving.

There is no home treatment for a molar pregnancy.

If you have had a molar pregnancy, use highly effective birth control measures to prevent pregnancy during the 6 to 12 months following treatment, according to your doctor's advice. For more information on contraception, see the topic Birth Control.

• Birth Control
• Grief and Grieving
• Preeclampsia and High Blood Pressure During Pregnancy

Citations

1. Berkowitz RS, Goldstein DP (2007). Gestational trophoblastic disease. In JS Berek, ed., Berek and Novak's Gynecology, 14th ed., pp. 1581–1603. Philadelphia: Lippincott Williams and Wilkins.

2. Cunningham FG, et al. (2005). Gestational trophoblastic disease. In Williams Obstetrics, 22nd ed., pp. 273–284. New York: McGraw-Hill.

3. Wax JR, et al. (2003). Prenatal diagnosis by DNA polymorphism analysis of complete mole with coexisting twin. American Journal of Obstetrics and Gynecology, 188: 1105–1106.

4. Berkowitz RS, et al. (1998). Recent advances in gestational trophoblastic disease. Current Opinion in Obstetrics and Gynecology, 10: 61–64.

5. Burtness B (2004). Neoplastic diseases. In G Burrow et al., eds., Medical Complications During Pregnancy, 6th ed., pp. 479–504. Philadelphia: Elsevier.

6. Berkowitz RS, et al. (2000). Management of gestational trophoblastic diseases: Subsequent pregnancy experience. Seminars in Oncology, 27(6): 678–685.

Other Works Consulted

• Aghajanian P (2007). Gestational trophoblastic diseases. In AH DeCherney et al., eds., Current Diagnosis and Treatment Obstetrics and Gynecology, 10th ed., pp. 885–895. New York: McGraw-Hill.