A molar pregnancy results from problems that occur when sperm fertilize an egg. In a typical pregnancy, a placenta forms to nourish the growing embryo. A placenta doesn’t form normally in molar pregnancies. Most people receive treatment and go on to have healthy future pregnancies.
A molar pregnancy occurs when an egg and sperm join incorrectly at fertilization and create a noncancerous tumor. The tumor looks like tiny water-filled sacs, similar to a cluster of grapes. The tumor can’t support a developing embryo and the pregnancy ends. Some people have a miscarriage. If this doesn’t happen, surgery is needed to remove the pregnancy. If left untreated, molar pregnancies can cause serious complications.
Molar pregnancies are a type of gestational trophoblastic disease. Gestational trophoblastic disease (GTD) is a group of conditions that cause tumors to grow in your uterus. Molar pregnancies are also called hydatidiform moles.
Molar pregnancies fall into two categories: complete and partial.
In complete molar pregnancies, no embryo forms. It happens when a sperm fertilizes an empty egg. Because the egg is empty, the embryo can’t grow. The placental tissue grows but is abnormal and contains fluid-filled cysts (or tumors). This tissue produces the pregnancy hormone HCG (human chorionic gonadotropin), which is made by a healthy placenta during pregnancy. This can make you feel like you’re pregnant and give you a positive pregnancy test.
A partial molar pregnancy occurs when an abnormal placenta forms along with an embryo, and two sperm fertilize one egg. In these cases, the growing embryo has an extra set of chromosomes. The embryo may start to develop but generally can’t survive.
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Although molar pregnancies are rare, anyone can have a molar pregnancy. You’re more likely to have a molar pregnancy if you:
Less than 1% of all pregnancies — about 1 in 1,000 — are molar pregnancies.
Unfortunately, a molar pregnancy results in the loss of the pregnancy.
Some people don’t have any symptoms of a molar pregnancy. For those who do, the most common include:
These symptoms are similar to many other conditions. It’s best to report any unusual symptoms to your healthcare provider.
Molar pregnancies are caused by genetic errors that occur during the fertilization of an egg by a sperm. In a typical pregnancy, an embryo gets one set of chromosomes (23) from each parent for a total of 46 chromosomes. Chromosomes are structures that contain genes. Genes tell your body how to work.
Molar pregnancies contain an imbalance of chromosomes. In a complete molar pregnancy, the egg contains no chromosomes. The embryo gets 23 chromosomes from the sperm. In a partial molar pregnancy, an egg is fertilized by two sperm. This results in the embryo having 69 chromosomes.
This genetic error leads to an unsuccessful pregnancy.
Your healthcare provider diagnoses a molar pregnancy during routine prenatal tests (usually in the first trimester). An ultrasound of your uterus often shows several fluid-filled sacs instead of a placenta. There’s usually no embryo or fetus in your uterus, but sometimes pregnancy tissue remains.
Your provider can also measure HCG levels in your blood. A healthy placenta produces HCG during pregnancy. It’s the hormone that at-home pregnancy tests measure in your urine (pee) to confirm a pregnancy. In molar pregnancies, HCG is produced at abnormally high levels. A blood test can detect these high levels and suggest a molar pregnancy has occurred.
Some people won’t have any symptoms of a molar pregnancy, and the diagnosis can be quite shocking. Just know that you did nothing to cause a molar pregnancy. In most cases, you can subsequently become pregnant with a healthy pregnancy if you chose to.
A molar pregnancy must be removed from your body or it can cause serious complications.
People generally require surgical treatment to remove molar pregnancies. Treatment involves dilation and curettage (D&C) with suction to remove all abnormal tissue from your uterus. General anesthesia is given so you don’t feel pain during this surgery.
In some cases, medication to help your uterus contract and expel the contents of your uterus is used instead of surgery. Talk to your healthcare provider about the best treatment option for you as urgent treatment is recommended for molar pregnancies to help prevent complications.
In very rare cases, a hysterectomy, or surgical removal of your uterus, is necessary to treat a molar pregnancy.
Your healthcare provider will monitor your HCG levels until levels return to normal. This ensures all the molar tissue is gone. HCG levels that don’t return to normal may indicate more serious complications.
Occasionally, parts of the molar pregnancy remain in your uterus after surgical treatment or miscarriage.
If this happens, abnormal cells may grow into the muscle layer around your uterus (also called an invasive mole). This is rare and happens in less than 15% of people who’ve had a molar pregnancy removed.
In very rare cases, molar pregnancy causes a type of cancer called choriocarcinoma. Choriocarcinoma forms within your uterus and may spread to other parts of your body and requires cancer treatments such as chemotherapy or radiation.
Other potential complications of a molar pregnancy include:
There’s no way to prevent a molar pregnancy. If you’ve had a molar pregnancy, you can reduce your likelihood of complications by avoiding another pregnancy for up to one year after your initial molar pregnancy. Talk to your pregnancy care provider about when it’s safe to begin trying to conceive.
Most people who receive treatment for a molar pregnancy have no further complications. If you have a molar pregnancy, your risk for miscarriage doesn’t increase. You’re only at a slightly higher risk of a second molar pregnancy.
Some people find it helpful to seek genetic counseling before conceiving again. There aren’t any indications that a molar pregnancy should affect your decision to try to conceive again if you wish to do so.
No, it doesn’t cause infertility. However, you should avoid becoming pregnant for up to three months. This allows your HCG levels to return to prepregnancy levels. Ask your pregnancy care provider about when you can begin trying for another pregnancy.
A molar pregnancy usually results in the loss of the pregnancy. It’s normal to be disappointed and sad that you aren’t pregnant. Take time to grieve the loss. Look for support from your family, friends or support groups that deal with losing a pregnancy. If you’ve had a molar pregnancy in the past, you’re likely to have a healthy pregnancy in the future.
If you’re pregnant and experiencing vaginal bleeding, severe nausea and vomiting, or passing grape-like cysts from your vagina, contact your pregnancy care provider immediately. Prompt evaluation and treatment are necessary to prevent complications.
A note from Cleveland Clinic
A molar pregnancy can be a traumatic and upsetting experience. Molar pregnancies result from genetic problems that occur during conception that are out of your control. It’s normal to have questions about what went wrong and to be fearful about future pregnancies. Talk to your healthcare provider about your concerns, ask them any questions you have and let your family and friends support you during this time. Most people go on to have healthy pregnancies.
Last reviewed by a Cleveland Clinic medical professional on 12/26/2022.
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