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How Does A Molar Pregnancy Happen?

How Does A Molar Pregnancy Happen?

A molar pregnancy is a condition where the egg is abnormally fertilized by two sperms. It is also known as Hydatidiform Mole, and is characterized by the irregular growth of the trophoblast cells, the cells which are developed within the placenta. Generally the number of chromosomes in human cells is 46 (23 pairs) but sometime the number of chromosomes become 69 instead of 46. This happens when two sperms reach the egg simultaneously and fertilize a single egg, leaving extra genetic material from the father. Molar pregnancies are very rare and happen only in 1 out of 1000 females.

There are basically two types of molar pregnancies- Partial molar pregnancy and complete molar pregnancies. In complete molar pregnancy, there is abnormal and swollen placental tissue which appears to form cysts filled with fluid. The fetal tissue does not form at all. In partial molar pregnancy there are both normal placental tissue and the abnormal placental tissue. The fetus may also be formed but do not live for very long, there is a miscarriage in the early days.

How Does A Molar Pregnancy Happen?

Causes And Symptoms Of Molar Pregnancy

During the early stage of pregnancy, a molar pregnancy seems to be like normal pregnancies, but there are certain signs and symptoms which distinguishes the normal pregnancy and a molar pregnancy.

  • Red or dark brown vaginal bleeding during first three months
  • Extreme nausea and vomiting
  • Cysts, that of size of grapes which sometimes pass through vagina
  • Pelvic pain and pressure

If any of the above symptoms are visible, it might be a molar pregnancy and a doctor should be immediately consulted. The doctor will diagnose and may check the symptoms of molar pregnancy like:

The main cause of molar pregnancy is an abnormally fertilized egg. Generally the fertilized cell has 23 pair of chromosome. One chromosome in every pair comes from the mother and other chromosome comes from the father.

In the case of complete molar pregnancy the egg is fertilized by two sperms and the entire genetic material comes from both the sperms i.e. from father. In such cases the mother’s genetic material is destroyed, lost or inactivated and the father’s chromosomes’ get duplicated.

In case of incomplete or partial pregnancy the chromosomes from mother remain intact but two sets of chromosomes come from the father. This way there are three sets of chromosomes and the number of chromosomes becomes 69 instead of 46. This also happens when two sperms fertilize the same egg.

Molar pregnancies are likely to occur in 1 out of every 1000 females and usually happen when the pregnancy occurs at the age after 35 or before 20. If any female had a molar pregnancy earlier then she has chances of getting molar pregnancy again.

Complications And Preventions

Even after a molar pregnancy has been removed the molar tissue might continue to grow. This condition is known as Gestational Trophoblastic Neoplasia. It happens in around 15 to 20% cases of complete molar pregnancies and about 5% of incomplete or partial molar pregnancies. If there is a persistent GTN in females, it will be characterized by high level of human chorionic gonadotropin hormone, even after the pregnancy has been removed. There can be vaginal bleeding also.

Such cases can be treated successfully with Chemotherapy. Sometimes the persistent GTN may become malignant and may spread in other organs. In this way the treatment is done either through chemotherapy or removal of the ovary.


A molar pregnancy is a condition where the human egg is abnormally fertilized by two sperms. This happens when two sperms reach the egg simultaneously and fertilize a single egg, leaving extra genetic material from the father. A molar pregnancy can be seriously complicated if not treated on time. It can also cause a kind of rare cancer.


  1. American Pregnancy Association. (2021). Molar pregnancy: Symptoms, causes, and treatments. https://americanpregnancy.org/pregnancy-complications/molar-pregnancy/
  2. NHS. (2019). Molar pregnancy. https://www.nhs.uk/conditions/molar-pregnancy/

Also Read:

Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:January 16, 2024

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