After a conception occurs there are two bundles of cells which make up the pregnancy. The first half becomes the placenta and umbilical cord, the second half develops into the baby.
Sometimes the cells become jumbled during the division process and the process gets aborted before it has completed, resulting in the placenta developing, but no baby.
It is thought to be due to chromosomal abnormality. If a child develops it may be severely disabled and this is why the body stops the process before it has finished.
This phenomenon is surprisingly common and causes around 60% of miscarriages, although in the majority of these, the woman is not even aware she is pregnant, as the pregnancy aborts before she has even missed a period.
If either or both partners have genetically abnormal sperm or eggs and have suffered recurrent miscarriage, it could be due to the fact that only the placenta has formed.
What is a Molar Pregnancy?
A molar pregnancy is an extension of the condition, where the body fails to miscarry the placenta and instead, it becomes cancerous. This is called a Hydatidiform mole, hence the term molar pregnancy.
Some women eventually pass the mole and suffer no adverse health effects, but for others it remains and would need to be surgically removed.
Around one in 2,000 women have a molar pregnancy that does not abort before their period is due, and for Asian women, this is much more common, at one in 200 pregnant women.
What are the Symptoms of a Molar Pregnancy?
Due to the placenta being present, the body still produces the pregnancy hormone, HCG, so very often the woman will believe she is having a normal pregnancy because she will have normal pregnancy symptoms including morning sickness, absent periods and sore breasts.
The first sign of a molar pregnancy is usually when the uterus fails to grow at the expected rate. Other signs include:
- Abnormally bloated uterus due to the tumor
- Passing unusual tissue
- Abnormally high levels of HCG for the stage of pregnancy
- Pre-eclampsia - this is very common in women with molar pregnancies
- Lots of cysts showing on ultrasound but no sight of the baby
- Vaginal bleeding
- Severe vomiting.
If a molar pregnancy is confirmed it will be removed.
Cancer and Infertility Risks From the Hydatidiform Mole
2 to 3% of women who have a molar pregnancy go on to develop a more aggressive form of cancer called Invasive mole or another form of cancer, choriocarcinoma, which can develop after a hydatidiform mole.
Sometimes a woman can develop a tumor at the site of the placenta after it has been removed. This is called a placental site trophoblastic tumor.
If any of these cancerous conditions occur, they will be removed by curettage. You will then be offered chemotherapy. This unfortunately can cause infertility. If you still want to try and have a baby, a single dose chemotherapy drug is available which may have less of a negative impact on your fertility.
If the disease is persistent, you may be offered hormonal contraception to suppress it.
1% of women who have had a molar pregnancy develop the condition again in a subsequent pregnancy but the good news is the majority of cases can be cured.
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