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Molar Pregnancy

Molar Pregnancy - What it is

What is a molar pregnancy?
In a normal pregnancy, a sperm fertilises an egg which grows to become an embryo (baby). The sperm and egg each has half the genetic material from the father and mother respectively.

A molar pregnancy, also known as a hydatidiform mole, is an abnormal pregnancy where there is an imbalance in the amount of genetic materials from the egg and the sperm. As a result, the fertilised egg cannot survive and does not develop into a baby.

It is rare and occurs in about one in 600 pregnancies.

There are two kinds of molar pregnancy:
Complete mole

  • This happens when one sperm fertilises an ‘empty’ egg (which has no genetic materials). The sperm divides to give the egg an equal amount of genetic material, all of which come from the father.
  • Occasionally, this can also occur when two sperms fertilise an ‘empty’ egg.

Partial mole

  • This happens when two sperms fertilise a normal egg and the fertilised egg has three sets of genetic material or more. This may develop into a fetus, but due to the abnormality as a result of the fertilisation process, the fetus does not develop further.

When is a molar pregnancy suspected?
Some women may have no symptoms at all.

Some may have symptoms which include:

  • Vaginal bleeding that can be irregular or heavy.
  • Excessive nausea or vomiting
  • The womb may be bigger in size than expected
  • Unable to confirm a viable pregnancy on scan

Other less common symptoms include high blood pressure, fast heart rate, overactive thyroid gland, abdominal pain due to large cysts in the ovaries.

Why do I have a molar pregnancy?
The exact cause of molar pregnancy is unclear. However, there are certain factors that can increase the chance of getting a molar pregnancy.

  • Age: They are more common in teenagers or women more than 40 years old
  • Race: They are twice as common in Asians as compared to non-Asians.
  • Previous molar pregnancy
  • Family history: Very rarely, some women in the same family have molar pregnancies.

What tests will be done if a molar pregnancy is suspected?
A blood test is done to measure the human chorionic gonadotrophin (bHCG) level which is a hormone produced by the pregnancy. Usually, the levels are much higher than a healthy pregnancy.

An ultrasound scan of the womb will be done. If it is a complete mole, there will be no baby seen but there are other signs to suggest a molar pregnancy. If it is a partial mole, a fetus may be seen. The pregnancy tissues will need to be examined by a pathologist before diagnosis of a partial mole can be made.

Further investigations such as additional blood tests or a chest x-ray may be necessary depending on your condition.

The treatment for molar pregnancy is evacuation of the uterus (womb) which is a surgical procedure to remove the pregnancy tissues.

After the surgery, the tissues are examined by the pathologist to confirm the diagnosis.

Do I need anti-D?
If your blood group is rhesus negative and your partner’s blood group is rhesus positive, you will require an injection called anti-D to prevent the formation of proteins (antibodies) that can affect future pregnancies.

What is the follow-up after the treatment?
You will be seen in a dedicated clinic for women with molar pregnancies.

There will be regular follow-ups where you will need to do blood tests until the bHCG level has returned to normal.

Once the bHCG level is normal, you will need further blood or urine tests to ensure that there is no more molar tissues in your womb. The duration of the follow-up period depends on whether you have a complete mole or a partial mole. Please check with your doctor regarding the exact duration.

It is important to attend every follow-up as some women will develop persistent disease which requires further treatment (chemotherapy).

For a complete mole, the risk of requiring further treatment is 15% while for a partial mole, the risk of requiring further treatment is 0.5%.

When can I get pregnant again?
A molar pregnancy does not affect your ability to get pregnant subsequently. However, you should only get pregnant after you have completed your follow-up. This is because a new pregnancy can mask the persistence or growth of the molar pregnancy cells which will affect the detection and treatment of these cells.

What birth control methods can I use during the follow-up?
You are advised to use birth control until your follow-up is complete. The following forms of contraception are suitable to be used during the follow-up:

  1. Barrier methods (condoms)
  2. Oral contraceptive pills/Progesterone-only pills
  3. Depo-provera
  4. Implanon

For intrauterine contraceptive devices (IUCD) such as the copper IUCD and levonorgestrel IUCD (e.g. Mirena®), they can only be used when your bHCG levels have returned to normal due to the risk of uterus (womb) perforation during insertion.

What are the risk of getting another molar pregnancy?
The chance of a molar pregnancy occurring again is one in 801 women.

What do I need to to be aware of for future pregnancies?
There is nothing you can do to prevent or reduce the risk of a molar pregnancy.

For all future pregnancies, you need an early ultrasound scan of the womb to check for recurrence. A bHCG blood test six to eight weeks should also be performed after any subsequent pregnancy including an abortion, miscarriage, ectopic pregnancy, or a live birth.

What is gestational trophoblastic neoplasia (GTN)?
Occasionally after a molar pregnancy, it can persist and develop into a cancerous form called GTN. The cells grow rapidly and can spread to other parts of the body such as the lungs, liver and brain. There are various types of GTNs and they include invasive mole, choriocarcinoma, placental site trophoblastic tumour and epitheliod trophoblastic tumour. Treatment of GTN is very successful with chemotherapy and the chance of cure is excellent.

GTN can occur after any pregnancies including abortions, miscarriages or a live birth. It is usually diagnosed when the bHCG level does not decrease to normal.

What happens if I have GTN?
It is rare to have GTN. If you do, you will be referred to our gynaecology oncologist for further management. Investigations such as blood tests and a computed tomography (CT) scan will be ordered before starting treatment. After treatment is completed, you will be on long term follow-up and will need to wait for at least one year before trying to get pregnant.

When should I return?
Please seek medical attention if you:

  • Have abnormal vaginal bleeding such as irregular, heavy bleeding
  • Feel breathless or cough up blood
  • Have unusual headaches • Have any concerns or queries that you want to ask your doctor


  1. Royal College of Obstetricians and Gynaecologists. 2010. Green Top Guideline No 38: Gestational Trophoblastic Disease. Retrieved from

The information above is also available for download in pdf format.

Molar Pregnancy - Symptoms

Molar Pregnancy - How to prevent?

Molar Pregnancy - Causes and Risk Factors

Molar Pregnancy - Diagnosis

Molar Pregnancy - Treatments

Molar Pregnancy - Preparing for surgery

Molar Pregnancy - Post-surgery care

Molar Pregnancy - Other Information

The information provided is not intended as medical advice. Terms of use. Information provided by SingHealth