Hydatidiform mole

Causes

What causes hydatidiform moles?

A hydatidiform mole is a pregnancy that starts with the wrong amount of genetic information (chromosomes). It is also called a molar pregnancy. Our genetic information holds the instructions for the body to grow and develop normally. The genetic information is packaged into structures called chromosomes. In humans, most cells contain 23 pairs of chromosomes, or 46 total chromosomes. The two types of molar pregnancies are called complete and partial.

In pregnancy, an egg is fertilized by the sperm. Usually, the egg and sperm each provide half of the chromosomes. In a complete molar pregnancy, the egg is missing its chromosomes. The missing information is replaced by either making a second copy of the chromosomes from the sperm or being fertilized by two sperm. The resulting pregnancy doesn't have any genetic information from the mother, only the father. Without genetic information from the mother, a baby cannot develop. The fertilized egg grows into a mass of tissue that implants in the uterus. On ultrasound this mass looks like a cluster of grapes. There are no signs of a fetus. The growth of the mass is considered a type of tumor that is usually not cancerous. It is called gestational trophoblastic disease. However, without treatment and complete removal, it can become cancerous. This happens about 15-20% of the time.

Partial molar pregnancies usually happen when an egg is fertilized by two sperm. It can also happen when an egg is fertilized by one sperm that duplicates its genetic information. This results in a pregnancy that has too many sets of chromosomes. It can't develop normally due to the extra information. On ultrasound the placenta looks like a cluster of grapes and there is a fetus developing. The fetus has many growth problems and birth defects. The fetus typically dies within a few weeks of conception. Partial molar pregnancies have a small chance of becoming cancer, but this is uncommon.

Hydatidiform moles happen randomly. They occur due to problems with the fertilization process. The exact cause is unknown. A parent cannot do anything that would cause one to occur. There is also nothing that can be done to prevent them from happening. Talk to your doctor to find out more about what causes hydatidiform moles. The type of doctor who manages pregnancy is called an obstetrician. To find an obstetrician near you, use the Find an OB-Gyn tool on the American College of Obstetricians and Gynecologists website.

References
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Why can't a hydatidiform mole develop into a baby?

Are there different types of hydatidiform moles?

Are there genes related to recurrent hydatidiform mole?

How do mutations in NLRP7 and KHDC3L cause recurrent hydatidiform moles?

Which gene mutation is the most common in recurrent hydatidiform moles?

Why can't a hydatidiform mole develop into a baby?

Hydatidiform moles are usually caused by abnormal fertilization of an egg. In some cases, the egg is has no genetic information. When it is fertilized by the sperm, it is missing half of the instructions it needs to grow and develop normally. Without these genetic instructions, the baby cannot develop. In other cases, two sperm fertilize the egg. This results in too much genetic information. These extra instructions cause problems with the growth and development of the baby. Ask your doctor to find out more about how a baby develops. The type of doctor who manages pregnancy is called an obstetrician. To find an obstetrician near you, use the Find an OB-Gyn tool on the American College of Obstetricians and Gynecologists website.

Are there different types of hydatidiform moles?

There are two types of molar pregnancies: complete and partial. A hydatidiform mole or molar pregnancy is a pregnancy that begins with the wrong amount of genetic information from the time the egg and sperm come together. In humans, most cells contain 23 pairs of chromosomes, or 46 total chromosomes. The chromosomes carry important genetic information needed for the body to grow and develop normally.

Complete molar pregnancies happen when the egg is missing its chromosomes and it "makes up" for that loss by either doubling the chromosomes from the sperm or being fertilized by two sperm. The resulting pregnancy doesn't have any genetic information from the mother, only the father. This results in the growth of a large mass of tissue implanting and growing in the uterus. On ultrasound this mass looks like a cluster of grapes without any sign of a fetus.

Partial molar pregnancies usually happen when an egg is fertilized by two sperm or by one sperm which duplicates its genetic information. This results in a pregnancy that has too many sets of chromosomes and can't develop normally. On ultrasound this placenta looks like a cluster of grapes and there is a fetus developing (usually with many growth problems and birth defects).

Ask your doctor to find out more about the different types of molar pregnancies. The type of doctor who manages pregnancy is called an obstetrician. To find an obstetrician near you, use the Find an OB-Gyn tool on the American College of Obstetricians and Gynecologists website.

References
Are there genes related to recurrent hydatidiform mole?

Most of the time, women do not have more than one hydatidiform mole (molar pregnancy). However, sometimes a woman can have more than one. When a woman has multiple molar pregnancies, it is called recurrent hydatidiform mole (molar pregnancy). Recurrent molar pregnancy has been linked to mutations in two different genes. These genes are called NLRP7 and KHDC3L. Both of these genes are involved with turning off other genes when they are not needed. This is how the body makes sure that the correct genes and proteins are expressed during development. When NLRP7 and KHDC3L are not working correctly, they cannot turn the other genes on and off at the correct times. This results in the wrong amount of genetic information being expressed. The pregnancy cannot grow and develop correctly due to having the wrong amount of genetic information. Talk to a genetic counselor to learn more about the genes involved in recurrent molar pregnancy. Genetic counselors assist in understanding genetic information. To find a genetic counselor near you, visit the Find a Genetic Counselor tool on the National Society of Genetic Counselors website.

How do mutations in NLRP7 and KHDC3L cause recurrent hydatidiform moles?

Most of the time, women do not have more than one hydatidiform mole (molar pregnancy). However, sometimes a woman can have more than one. Mutations in the NLRP7 and KHDC3L genes can increase the chance of having more than one molar pregnancy (recurrent molar pregnancy). NLRP7 and KHDC3L are responsible for turning certain genes off during development. Mutations in NLRP7 and KHDC3L can cause them to be unable to do this. Due to this impaired function, many genes that are normally "turned off" during development are active. This results in abnormal development of the embryo, which causes an increased chance to have a molar pregnancy. Talk to a genetic counselor to learn more about how these genes work. To find a genetic counselor near you, visit the Find a Genetic Counselor tool on the National Society of Genetic Counselors website.

Which gene mutation is the most common in recurrent hydatidiform moles?

Most of the time, women do not have more than one hydatidiform mole (molar pregnancy). However, sometimes a woman can have more than one. Mutations in the NLRP7 and KHDC3L genes can increase the chance of having more than one molar pregnancy (recurrent molar pregnancy). 1-6% of women with a previous molar pregnancy will have more. The NLRP7 mutation is the most common cause of recurrent hydatidiform moles. Talk to a genetic counselor to learn more about how these genes work. To find a genetic counselor near you, visit the Find a Genetic Counselor tool on the National Society of Genetic Counselors website.

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