Molar pregnancy or hydatidiform mole is an abnormality of the placental cells (trophoblastic cells which normally develop into the placenta) which occur during the fertilization of the egg and sperm. Abnormal cells or clusters of cells filled with water will grow in the uterus. Molar pregnancies occur 1 out of every 1000 pregnancies in United States, 1 in 590 pregnancies in UK, 1 out of 100 pregnancies in Indonesia, and 1 out of 200 pregnancies in Mexico. The incidence varies in different parts of the world, this can be due to the different study methodology used in the studies.
How Common Is Partial Molar Pregnancy?
Partial molar pregnancy occurs when the egg is fertilized by two sperms which result in an embryo with 69 chromosomes. The normal chromosomes in an embryo is 46 chromosomes. In these 69 chromosomes one set (23 chromosomes) is from the mother and the other two sets are from the father. The fetus can develop but it will have severe birth defects and usually dies within 3 months of gestation due to the birth defects. An abnormal cell mass will also develop and it will grow rapidly overcoming the development of the fetus.
Partial molar pregnancies are 2 to 3 times commoner than the complete molar pregnancies. An exact incidence of partial molar pregnancies is not present in the literature; however, it is believed to be more common than the complete molar pregnancies and it also causes few complications compared to the complete molar pregnancy. Partial molar pregnancy with coexisting fetus is a very rare complication and the incidence is about 0.005-0.01% out of all pregnancies.
Risk Factors For Partial Molar Pregnancy
Having a risk factor or several risk factors does not mean that you will definitely get the disease. It’s that you have an increased risk in getting that particular disease compared to the general population. Sometimes people who don’t have any risk factors also gets the disease. So, if you have any of the following risk factors the chance of you getting a molar pregnancy is high. But that does not necessarily mean you will definitely get it.
Age. Age is not considered as a risk factor for partial molar pregnancy. Research studies have not found any correlation between the age and occurrence of partial molar pregnancy
Previous Molar Pregnancy. If you had a molar pregnancy previously there is about 1-2% chance of getting it in the future pregnancies. If you had more than one molar pregnancy the risk is higher usually about 15-20%.
Prior Miscarriage. Women who had previous miscarriages have an increased risk of getting molar pregnancies. The reason might be the miscarriage occurred due to a molar pregnancy itself. However, the overall risk of molar pregnancy after a miscarriage is still low.
Blood Type. Women with blood group A or AB are at a higher risk.
Oral Contraceptive Pills. If you are on oral contraceptive pills (OCP) you at high risk of developing a molar pregnancy. Women who have used OCP for a longer time have a higher risk, however this risk is very low and it outweighs the benefits of using the pill. The exact reason how OCP increases the risk is unknown.
Family History. Sometime women with a family history develop molar pregnancy. Although no specific gene is still not found.
Conclusion
Molar pregnancies occur 1 out of every 1000 pregnancies in United States, 1 in 590 pregnancies in UK, 1 out of 100 pregnancies in Indonesia, and 1 out of 200 pregnancies in Mexico. The incidence varies in different parts of the world this can be due to the different study methodology used in the studies. Partial molar pregnancies are 2-3 times commoner than the complete molar pregnancies. An exact incidence of partial molar pregnancies is not present in the literature; however, it’s believed to be more common than the complete molar pregnancies and it also causes few complications compared to the complete molar pregnancy. Partial molar pregnancy with coexisting fetus is a very rare complication and the incidence is about 0.005-0.01% out of all pregnancies.
- “Molar Pregnancy (Hydatidiform Mole).” Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/molar-pregnancy/symptoms-causes/syc-20375191
- “Molar Pregnancy: What You Need to Know.” American Pregnancy Association. https://americanpregnancy.org/pregnancy-complications/molar-pregnancy/
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