What is a Molar pregnancy?
What is a molar pregnancy, and if you’ve experienced one, is it more likely to happen again?
What is a molar pregnancy?
A molar pregnancy is a rare complication of pregnancy and is a form of miscarriage. Placental cells called trophoblasts grow abnormally. Sometimes in the medical literature, a molar pregnancy can be called a hydatidiform mole.
There are two types of molar pregnancy, complete molar pregnancy and partial molar pregnancy.
In a complete molar pregnancy, there is no fetus and placental tissue swells and appears to form hydopic, fluid-filled cysts.
In a partial molar pregnancy, placental tissue is very abnormal, there may be a fetus, but the fetus can't survive and usually stops developing early on, even if the pregnancy itself persists.
Why are molar pregnancies different to other types of miscarriages?
A molar pregnancy can have serious complications, including the development into a rare form of cancer. A molar pregnancy requires early intervention, treatment and long term follow up.
What are the symptoms of molar pregnancy?
A molar pregnancy may seem like a regular pregnancy at first and symptoms of molar pregnancy can be non-specific.
Symptoms of molar pregnancy can include:
Early pregnancy bleeding
Severe nausea and vomiting (known as hyperemesis gravidarum)
Sometimes grape-like cysts may pass via the vagina
Pelvic pressure or pain
If undiagnosed until later in pregnancy, molar pregnancy can present with the following symptoms:
A uterus growing too quickly, faster than expected for the stage of pregnancy.
Preeclampsia before 20 weeks gestation, a condition associated with high blood pressure and protein leak in the urine.
Ovarian cysts
Hyperthyroidism (thyroid over activity, driven by the hormone HCG)
What causes a molar pregnancy?
In a normally fertilized egg, 50% of the DNA present comes from the sperm, with the other half from the egg.
In a complete molar pregnancy, one or two sperm fertilize an egg. The egg’s DNA contribution is lost and the sperms chromosomes are copied. No DNA from the egg contributes to a complete molar pregnancy.
In a partial (incomplete) molar pregnancy, the egg’s chromosomes are present, but the sperm supplies two sets of chromosomes (2 sperm fertilise the egg). In effect, the pregnancy has 3 sets of chromosomes.
Are there any risk factors for having a molar pregnancy?
Risk factors for a molar pregnancy include:
Past history of a molar pregnancy. The recurrence risk for molar pregnancy is 1% (1 in 100). The background population risk of molar pregnancy is 1 in 200-1000 pregnancies.
Age of the mother. Extremes of maternal age are associated with a higher risk of molar pregnancy (if a mother is aged under 15 years or over 43 years)
How can a molar pregnancy become a cancer?
When molar tissue persists after the removal of a molar pregnancy, this is called persistent gestational trophoblastic neoplasia (GTN).
GTN is more common in complete molar pregnancies. A sign is a persistently high level of the pregnancy hormone bHCG. In some cases, molar pregnancy tissue invades the muscle wall of the uterus. Persistent GTN is usually treated with chemotherapy or by surgical removal of the uterus (hysterectomy).
Choriocarcinoma is a malignant form of GTN that can spread to distant organs in the body such as liver and lung. If untreated, this contition will be fatal to the mother. Choriocarcinoma is usually successfully treated with chemotherapy.
To make sure a molare pregnancy has fully resolved we track a woman’s HCG hormone level to zero. It may be recommended that a future pregnancy be delayed for 6-12 months after a serious molar pregnancy as we have no way of telling if an HCG rise is due to a cancer recurrence versus a new pregnancy.
Can a woman do anything to make sure another molar pregnancy doesn’t happen?
If you have to delay getting pregnant again and want to make sure you don’t have another molar pregnancy – we can create embryos for you through IVF that can be genetically tested by PGT (preimplantation genetic testing) before embryo trnasfer to make sure another molar pregnancy doesn’t happen.
For more on molar pregnancies, listen to this episode of the Knocked Up podcast
Written by Dr Raelia Lew
RANZCOG Board Certified CREI Fertility specialist, Gynaecologist and the Director of Women’s Health Melbourne.
Co-host of the Knocked Up Podcast, Co-founder of Lovers intimate wellness solutions. Raelia has a PhD in Preconception Health Promotion and Genetic Screening. Raelia is a leading Australian expert in IVF and egg freezing, pioneering a bespoke model of care.