Why Does A Molar Pregnancy Happen?

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What is a molar pregnancy?

A molar pregnancy also known as gestational trophoblastic disease (GTD), hydatidiform mole or simply “mole”  and is due to the abnormality of the placenta, caused when the egg and sperm join together at the time of fertilization. These are rare, occurring in 1 out of every 1,000 pregnancies. A genetic error during fertilization process may lead to the growth of abnormal tissue within the uterus which is referred as molar pregnancy. Other than rarely involving the development of an embryo, the growth of this material is compared to the normal fetal growth. The appearance of the tissue is like the large and random collection of grape-like cell clusters. Molar pregnancies are of two types; “complete” and “partial.”

Complete molar pregnancy

Complete molar pregnancies have only placental parts and is formed when the sperm fertilizes an empty egg. Since the egg is empty, no baby is formed. The placenta grows and produces the pregnancy hormone, hCG or human chorionic gonadotropin. An ultrasound test will show that there is no fetus and only placenta is present.

Partial molar pregnancy

  • When the mass contains both the abnormal cells and an embryo with severe birth defects, the condition is referred as partial molar pregnancy.
  • An extremely rare version of a partial mole occurs when twins are conceived and only one embryo begins to develop normally, while the other is a mole. In such cases, the healthy embryo will be gradually consumed by the abnormal growth.


Who is at risk for a molar pregnancy?

  • Approximately 1 out of 1,000 pregnancies in US is a molar pregnancy
  • Mexico, Southeast Asia, and the Philippines have higher rates than the US in case of molar pregnancy.
  • White women in the US are at higher risk than black women
  • Women over the age of 40
  • Women who have previous history in molar pregnancy
  • Women with a history of miscarriage

Symptoms of a molar pregnancy

  • Vaginal bleeding
  • Nausea and vomiting
  • Develop rare complications like thyroid disease
  • Early preeclampsia (high blood pressure)
  • Increased hCG levels
  • No fetal movement or heart tone detected

How to detect molar pregnancy?

  • A pelvic exam can detect larger or smaller uterus, enlarged ovaries, and abnormally high amounts of the pregnancy hormone hCG.
  • A sonogram is helpful in detecting “cluster of grapes” appearance, signifying an abnormal placenta.

How is a molar pregnancy treated?

  • Most of the molar pregnancies have a spontaneous end and the expelled tissue will appear grape-like.
  • Molar pregnancies can be removed by suction curettage, dilation and evacuation or sometimes through medication.
  • Approximately 90% of women who have removed the mole require no further treatment.
  • Follow-up procedure is done to ensure that the mole has been removed completely. Traces of the mole may begin again and may possess a cancerous-type threat to other parts of the body.
  • Pregnancy must be avoided for one year after a molar pregnancy.
  • Any birth control method is acceptable with the exception of an intrauterine device.

Emotional effect of molar pregnancy


The condition when an embryo is present which do not have an ability to develop into a child can be regarded as a significant loss. Most women discover that they are dealing with a molar pregnancy after the discovery and anticipation of being pregnant. As the dreams, plans and hopes are cancelled all at once, molar pregnancy also has an emotional side on other side. Support groups and counseling may be beneficial at this stage.

Can I have another molar pregnancy?

  • If one had a molar pregnancy without any complication, the risk of having another molar pregnancy is reduced to about 1-2%.
  • Genetic counseling prior to conceiving again is helpful for some couples.