What is a Molar Pregnancy?
A molar pregnancy is an uncommon condition in which your uterus becomes “pregnant” with an abnormal growth instead of a viable embryo. Even though it feels like a normal pregnancy, the growth will not develop into a fetus. An abnormality of the placenta, a molar pregnancy is caused by a problem when the egg and sperm join together at fertilization. Molar pregnancies are rare, occurring in 1 out of every 1,000 pregnancies. Molar pregnancies are also called gestational trophoblastic neoplasia (GTN), hydatidiform mole or simply referred to as a “mole.” A molar pregnancy is a risk factor for the development of persistent gestational trophoblastic neoplasia (GTN).
A molar pregnancy is the result of a genetic error during the fertilization process that leads to a growth of abnormal tissue within the uterus. Molar pregnancies rarely involve a developing embryo, and the growth of this material is rapid compared to normal fetal growth. It has the appearance of a large and random collection of grape-like cell clusters. There are two types of molar pregnancies, “complete,” and “partial.”
A partial molar pregnancy is when two sperm fertilizes the same egg. The cells of the partial molar tissue will start to divide, creating a malformed embryo and some placental tissue, but they will not survive.
When a sperm fertilizes an abnormal egg containing no genetic information, this is known as a complete molar pregnancy. Complete molar pregnancies have only placental parts (there is no baby) and form when the sperm fertilizes an empty egg. Because the egg is empty, no baby is formed. The placenta grows and produces the pregnancy hormone, human chorionic gonadotropin (hCG). Unfortunately, an ultrasound will show that there is no fetus, only a placenta. In a complete molar pregnancy, the placental tissue is abnormal and swollen and appears to form fluid-filled cysts. There’s also no formation of fetal tissue.
Neither of these conditions has the correct genetic information to become a viable embryo.
Complications of a Molar Pregnancy
The abnormal tissue must be removed right away. Although most of these growths are benign, they can sometimes become harmful tumors.
If some molar tissue still remains even after removal, it may continue to grow and become cancerous. This complication occurs in about one out of five molar pregnancies.
The fertilized egg triggers a pregnancy response in your body, which starts producing hormones to prepare for pregnancy. If your doctor detects elevated hCG levels in your blood, it could mean that you still have some molar tissue growing in your uterus. This is known as a persistent gestational trophoblastic disease (GTD).
The cause of a molar pregnancy is an abnormality during fertilization, likely when two sets of chromosomes from the father become mixed in with either one set of chromosomes from the mother (partial mole) — or none of her chromosomes at all (complete mole). Most molar pregnancies are discovered within weeks of conception, and all end in early pregnancy loss or miscarriage.
Signs and Symptoms of a Molar Pregnancy
At first, the condition may seem like a normal pregnancy. You might get morning sickness or miss your period. Symptoms of a partial molar pregnancy include severe nausea, vomiting, and hypertension (high blood pressure) early in the pregnancy, often in the first trimester. But usually, you will see other distressing symptoms, such as:
- Vaginal bleeding
- Pressure in the pelvis
- Nausea and vomiting
- Fast or irregular heartbeat
- Vaginal passing of tissue, especially grape-shaped cysts
If you’re experiencing these symptoms, contact your women’s health care provider. We will conduct a blood test and an ultrasound exam to confirm your diagnosis.
What Will an Ultrasound of a Molar Pregnancy Show?
The condition can usually be detected by 8 weeks. An ultrasound of a complete molar pregnancy will show:
- No embryo or fetus
- Cysts filling the uterus
- Ovarian cysts
- No amniotic fluid
A partial molar pregnancy will look much different. You will see:
- A malformed fetus
- Little amniotic fluid
- A cystic placenta
We understand that this could be a very difficult situation, physically as well as emotionally. We want you to feel comfortable asking questions and expressing your concerns. If you would like to try for pregnancy again, be aware that having a molar pregnancy does increase the likelihood that you will have another.
Patients are advised not to conceive for half a year after hCG levels have normalized. The chances of having another molar pregnancy are lower.
Management is more complicated when the mole occurs together with one or more normal fetuses.
Please bring any questions you may have, and your Ob/Gyn can discuss your future fertility options with you.