Molar pregnancy is the condition caused due to an error in the process of fertilization. This also results in abnormally higher concentration of hCG hormone.
What Is Molar Pregnancy hCG?
A hCG hormone is higher during pregnancy, but the level is even higher during complete molar pregnancy. Due to such higher level, the testing devices sometime give a false negative result. The level of hCG is comparatively lower in partial molar pregnancy as compared to complete molar pregnancy.
hCG (Human Chorionic Gonadotrophin) hormone is secreted by the placenta on conception i.e. when the fertilized egg is attached to the wall, the secretion of this hormone is initiated by the placenta. It is detected in the urine as early as six days after conception and can be measured through pregnancy testing strips. Test of this hormone can be done in both blood and urine. The level of this hormone is evaluated during pregnancy as well as to diagnose gestational trophoblastic diseases. Various forms of his hormone are present in the body. This includes nicked hCG, intact hCG, hyperglycosylated hCG, and free beta hCG. Out of these forms, the most analyzed form is beta-hCG. High level of his hormone is found during molar pregnancy.
However, this does not mean that a high level of hCG always means a molar pregnancy. It also does not mean that every molar pregnancy has abnormal levels of hCG. A complete molar pregnancy can be diagnosed through a high level of hCG along with other parameters as the levels in the condition is abruptly high and is more than 100000 IU/ml. However, diagnosis becomes difficult in case of partial molar pregnancy as the range of this hormone is wider and may also within the range of normal pregnancy.
Thus, the partial molar pregnancy condition is diagnosed by accessing histological parameters. However, it should also keep in mind that the diagnostic methods sometimes give false negative results for hCG incomplete molar pregnancy due to the hook effect. Hook effect is due to the oversaturation of signaling antibodies in the testing device.
Generally, the egg is released by the ovary and the sperm fertilizes the egg. This fertilized egg attaches to the placenta and the growth of fetus took place. The level of hCG is increased as it is secreted by placenta after conception. This is caused due to the error occurred during fertilization. The error may be the fertilization of a sperm with an egg which does not contain DNA. This results in a fertilized egg with no fetus. The other error may occur if two sperms fertilize an egg resulting in the combination of chromosomes of all the three haploid cells. This results in an unviable fetus with severe birth defects.
Pathophysiology Of Molar Pregnancy
Molar pregnancy, also known as hydatidiform mole, is characterized by the engagement of placental villi. The disease is a part of a larger disease known as gestational trophoblastic disease. The disease has a high rate of favorable prognosis due to two important reasons. First, the identification and diagnosis of the disease can be accurately done. hCG is an important marker for this disease. Second, the disease is highly responsive to drugs such as methotrexate. A molar pregnancy can be divided into two types on the basis of characteristics of the diseased tissues.
Complete Molar Pregnancy. In the complete molar pregnancy, the sperms fertilize with an empty egg. This means that there is no maternal substance present in the egg. The egg does not have DNA. In this case, the father’s chromosomes are duplicated as there are no mother chromosomes. These pregnancies only have the placental part and do not have a fetus. The concentration of hCG hormone increases due to the growth of the placenta. Ultrasound clearly indicates the absence of fetus and the growth of the placenta.
Partial Molar Pregnancy. In a partial molar pregnancy, there is a growth of incomplete fetus and placenta. The fetus formed in partial molar pregnancy has severe birth defects. It is due to the fact that partial molar pregnancy is caused when two sperms fertilize the egg. Thus the number of chromosomes in the fertilized egg is 69 as compared to 46 in the normal fertilized egg.
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- American Journal of Obstetrics and Gynecology: https://www.ajog.org/article/S0002-9378(14)01854-1/fulltext
- UpToDate: https://www.uptodate.com/contents/molar-pregnancy-diagnosis-and-management#H7
- Medscape: https://emedicine.medscape.com/article/271818-overview#a3