Human chorionic gonadotropin (hCG) is a pregnancy hormone that helps maintain pregnancy. The pregnancy test is based on the detection of this peptide hormone. Outside of pregnancy, elevated levels of chorionic gonadotropin indicate specific cancers.
What is human chorionic gonadotropin?
Human chorionic gonadotropin is usually produced in increased concentrations only during pregnancy. It is a two-subunit peptide hormone responsible for maintaining pregnancy. It is produced in human syncytiotrophoblasts. The syncytiotrophoblasts constitute a part of the placenta. The peptide hormone is a glycoprotein and consists of an alpha subunit with 92 amino acids and a beta subunit with 145 amino acids. The alpha subunit is also abbreviated as α-hCG and the beta subunit as β-hCG. Thereby, α-hCG also occurs as a part in other hormones such as thyrotropin (TSH), follicle stimulating hormone (FSH) or luteinizing hormone. However, the beta subunit (β-hCG) is only a component of human chorionic gonadotropin. During pregnancy, the concentration of this hormone increases continuously until the 10th to 12th week of pregnancy. Then the gradual decrease in the production of chorionic gonadotropin begins. Shortly before the 20th week of pregnancy, the concentration of human chorionic gonadotropin reaches a certain basal level, which is maintained until shortly after birth. After that, production of this hormone almost ceases. However, if human chorionic gonadotropin is detected in greater concentrations outside pregnancy, this forms an indication of carcinomas of the trophoblasts, ovaries, testes, liver, kidney, or even lungs.
Function, effects, and roles
The function of human chorionic gonadotropin is to maintain pregnancy. It prevents renewed ovulation and menstrual bleeding during pregnancy. This is achieved by human chorionic gonadotropin stimulating the corpus luteum in the ovary to produce progesterone. Progesterone builds up the uterine lining while signaling the pituitary gland to stop ovulating during pregnancy. The corpus luteum persists during pregnancy and can constantly produce progesterone during this time. It develops into the corpus luteum graviditatis. This prevents the degeneration of the corpus luteum. Until the 10th week of pregnancy, the corpus luteum graviditatis produces the pregnancy-maintaining hormones progesterone and estrogen under the influence of human chorionic gonadotropin. Thereafter, the placenta takes over this task, and the demand for chorionic gonadotropin slowly decreases again. The increased production of human chorionic gonadotropin begins approximately on the fifth day after fertilization. Initially, a hyperglycosylated form of the hormone is formed, which is necessary for the implantation of the blastocyst. Following the contact of the blastocytes with the uterine mucosa, trophoplast cells differentiate and the formation of the active form of human chorionic gonadotropin begins. The active human chorionic gonadotropin then stimulates the corpus luteum as described above.
Formation, occurrence, properties, and optimal levels
The formation of human chorionic gonadotropin occurs in the multinucleated syncytiotrophoblast of the placenta. The multinucleated syncytiotrophoblast is formed by the differentiation and profiling of some mononuclear cytotrophoblast cells of the blastocyst. Initially, the production of the hormone is low. However, it increases continuously from the fifth day of pregnancy. Thus, there are periods in pregnancy when the production of human chorionic gonadotropin doubles daily. The normal value of hCG in the blood is up to 5 IU/liter in men and non-pregnant women. After menopause, the normal value increases to 10 IU/liter in women. The rapid increase in the concentration of hCG begins, as already mentioned, from the fifth day after fertilization of the egg. Thus, by the third week of pregnancy, the value has already risen to just below 50 IU/liter. In the fourth week of pregnancy, a value of up to 400 IU/liter can already be recorded. The maximum concentration of human chorionic gonadotropin with approx. 230,000 IU/liter is reached in the tenth to twelfth week of pregnancy.Thereafter, the concentration of hGC slowly decreases again and reaches a value between 5000 and 65,000 IU/liter at the end of pregnancy. By the 17th day after pregnancy at the latest, the concentration of human chorionic gonadotropin has dropped back to normal. Therefore, as part of the pregnancy test, the progress of the pregnancy can be followed due to the changes in the concentration of the hormone.
Diseases and disorders
Determination of the concentration of human chorionic gonadotropin has great diagnostic significance. First, it serves as evidence of pregnancy and its progression. However, it can also be used to indicate a false pregnancy. In this case, increased human chorionic gonadotropin is indeed produced. However, the cause of increased values can also be a carcinoma of the ovaries, testicles, trophoblasts, kidneys, liver or even lungs. If the values are even more elevated during pregnancy, it may be a multiple pregnancy or an abnormality in the number of chromosomes. Thus, Down syndrome of the child is also indicated by an even more elevated concentration of human chorionic gonadotropin. However, if the concentration rises slowly during pregnancy and does not reach high levels, an ectopic or abdominal pregnancy may be present. Furthermore, low pregnancy concentrations of hCG may also indicate termination of pregnancy due to miscarriage, fetal death, missed abortion (unexpelled but dead fetus), impending premature birth, or gestosis. However, human chorionic gonadotropin can also be used as a drug in cases of missed menstrual periods, undescended testes, or infertility.
