Human chorionic gonadotropin (HCG), better known by its acronym hCG or even colloquially as "beta", is a glycoprotein synthesized in embryonic trophoblast cells. Specifically, hCG hormone is produced by the syncytiotrophoblast.
HCG consists of two distinct chains, one alpha (α) and one beta (ß). The beta chain is unique to hCG hormone; while the alpha subunit is identical to the alpha subunit of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and thyroid stimulating hormone (TSH).
Pregnancy tests are based on detecting hCG. The reason is that the presence of this hormone, when produced by the embryo, confirms gestation. In addition, these tests detect the beta subunit of hCG and, for this reason, the waiting period for the confirmation of pregnancy is commonly referred to as the waiting period beta-waiting.
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What is the function of the hCG hormone?
The purpose of hCG hormone is to promote the functionality of the corpus luteum, which is the remains of the ovarian follicle after ovulation. The corpus luteum secretes progesterone, and the hCG produced by the embryo itself is an indication that it maintains progesterone secretion until the placenta can take over this task.
Conversely, in the event that pregnancy has not occurred, the absence of hCG causes the corpus luteum to degenerate, which ultimately triggers menstruation.
HCG could also be involved in the development of maternal immunotolerance and thus prevent maternal immune rejection of the embryo during early gestation.
In addition, as mentioned above, the alpha subunit of this hormone is identical to that of LH and they have some biological similarities. For this reason, hCG is also used as a drug to induce ovulation in assisted reproduction treatments.
Why is it useful to detect the hCG hormone?
HCG is also known as the pregnancy hormone since its presence is indicative of pregnancy. Thus, pregnancy tests are based on evaluating the presence of hCG hormone in both urine and blood.
However, beta hCG screening to confirm possible pregnancy should not be done until there is a delay in menstruation or until at least 15 days have passed since intercourse. This allows time for the hormone to rise to levels detectable by the test.
On the other hand, in assisted reproduction treatments, a pregnancy test is usually performed after 10-15 days of beta waiting from the embryo transfer or artificial insemination.
In addition, altered levels of this hormone may be signs of genetic alterations in the fetus, such as Down syndrome. This is why free beta hCG levels are evaluated, along with other parameters, in the triple screening test performed in the first trimester of pregnancy.
Drugs containing hCG
As mentioned above, the hCG hormone can also be used as a drug in certain situations. In this case, there are two possible ways of obtaining this hormone for use as a hormone treatment:
- Urinary hCG or u-hCG: obtained from the urine of pregnant women and highly purified.
- Recombinant hCG or r-hCG: obtained by genetic engineering techniques.
However, with the introduction of genetic engineering and its evolution, the use of hCG of urinary origin was put on the back burner. Currently, the most common hCG drug is the Ovitrelle which contains recombinant hCG.
Use of hCG in assisted reproduction
HCG or human chorionic gonadotropin is used by women undergoing assisted reproduction treatment. This hormone is used to trigger the final maturation of follicles and ovulation.
The drug consists of a subcutaneous injection that the patient must frequently give herself. The woman will receive a series of indications from the gynecologist so that the administration is carried out correctly.
It is important to mention that this hormone should not be used without the supervision of an assisted reproduction specialist.
Effects of hCG
HCG is similar in structure and biological activity to luteinizing hormone or LH. In addition, both hormones share the same receptor in the theca and granulosa cells of the ovarian follicle.
For this reason, exogenous administration of hCG "simulates" the preovulatory LH peak that occurs during a normal menstrual cycle. Thus, hCG initiates a cascade of reactions that produces the following effects in the woman:
- Finalmaturation of the follicles and degradation of the follicular wall.
- Expulsion of the ovum, i.e. ovulation.
- Formation of the corpus luteum.
On the other hand, it should be noted that hCG induces ovulation about 36-40 hours after administration. Therefore, in in vitro fertilization (IVF) treatments, the ovarian puncture must be performed before this time is reached. Thus, mature oocytes are captured before they are released into the fallopian tube, as would occur in any menstrual cycle.
Indications for hCG
The use of this hormone is indicated in women undergoing assisted reproduction techniques, as it is used to plan and control when the release of eggs from the ovary occurs, as previously mentioned.
However, the administration of this hormone can also help women who have problems ovulating, such as oligoovulation or anovulation.
In any case, the administration of this hormone must be done under medical supervision and following all established guidelines.
Advantages and disadvantages of using hCG
The main advantage of drugs containing hCG is that this hormone promotes ovulation and, in addition, allows us to know exactly when ovulation will occur. Within 36 to 40 hours of hCG administration, the egg will be released.
This is extremely important in assisted reproduction because after the hCG injection, the rest of the treatment is programmed, whether it is follicular puncture or insemination.
In addition, this hormone supports the luteal phase. This means that hCG maintains the functionality of the corpus luteum for progesterone secretion.
However, the main drawback of the use of hCG hormone in assisted reproduction is the risk of ovarian hyperstimulation syndrome(OHSS). HCG has a vasodilator effect and can cause serious fluid extravasation problems if not controlled.
In this case, it could be very dangerous to have a pregnancy with acute OHSS, as the hCG produced naturally by the embryo would increase the harmful effects.
This is why, in those situations where there is a high concentration of estrogen before the ovarian puncture, the embryos obtained are frozen and transferred in another cycle. This is called deferred transfer and is a useful solution for OHSS cases, as it avoids the risks of getting pregnant in that cycle.
Side effects of hCG
Like any other medication, hCG injection may also cause some adverse reactions. Some of them are listed below:
- Headache.
- Pain and swelling in the abdomen.
- Nausea or even vomiting and diarrhea.
- Ovarian hyperstimulation syndrome (OHSS).
- Pain, swelling or irritation at the injection site.
- Allergic reactions, which may manifest with symptoms such as rash, swollen tongue or mouth, or difficulty breathing.
- Severe blood clotting problems.
If the patient is in any of these situations, it is best to consult a specialist as soon as possible to find out how to proceed.
FAQs from users
Why do I have hCG hormone in my blood if I am not pregnant?
The hCG hormone is produced almost exclusively in embryonic tissue, which is why it has been used for many years as the best biochemical marker that a woman is pregnant.
Now, can there be cases in which the patient has elevated hCG and is not pregnant? Indeed, this can happen, but most of these cases are actually due to miscarriages or abnormal pregnancies such as a biochemical pregnancy, ectopic pregnancy, etc.
Read more
What is the hCG pregnancy hormone used for?
Human chorionic gonadotropin (hCG) is a glycoprotein hormone produced both by the embryo and by the syncytiotrophoblast, a part of the placenta. The function of this hormone is to ensure that the embryo receives the nutritional and hormonal factors and protection necessary for its proper development.
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What are the causes of elevated hCG in the blood?
hCG is the hormone commonly known as the pregnancy hormone. Therefore, elevated levels of hCG in the blood would be indicative of pregnancy. Depending on what the exact value is, the exact weeks could be determined.
What is the mechanism of action of hCG?
The purpose of hCG hormone is to exert its function on the follicle, inducing its maturation. It also participates in the formation and maintenance of the corpus luteum in the ovary.
Another mechanism of action of hCG is to intervene in spermatogenesis, i.e. in the production of spermatozoa in men.
Can hCG be administered during lactation?
No. hCG hormone is not indicated in lactating women, since this hormone is secreted in the milk.
Which medicine contains hCG hormone?
The best known hCG drug is Ovitrelle, especially for ovulation induction in assisted reproduction treatments.
Recommended readings
For detailed information about beta hCG values in pregnancy, don't forget to visit this article: What are the normal values of beta-hCG hormone?
If you are interested in reading more about gonadotropins, we recommend you to access this link: Gonadotropins: What are they and what are their functions?
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References
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Choi J, Smitz J. Luteinizing hormone and human chorionic gonadotropin: distinguishing unique physiologic roles. Gynecol Endocrinol. 2014 Mar;30(3):174-81. (see)
Choi J, Smitz J. Luteinizing hormone and human chorionic gonadotropin: origins of difference. Mol Cell Endocrinol. 2014 Mar 5;383(1-2):203-13. (see)
Hay DL. Placental histology and the production of human choriogonadotrophin and its subunits in pregnancy. Br J Obstet Gynaecol. 1988 Dec;95(12):1268-75. (see)
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Vaitukaitis JL, Braunstein GD, Ross GT. A radioimmunoassay which specifically measures human chorionic gonadotropin in the presence of human luteinizing hormone. Am J Obstet Gynecol. 1972 Jul 15;113(6):751-8. (see)
Wang Z, Gao Y, Zhang D, Li Y, Luo L, Xu Y. Predictive value of serum β-human chorionic gonadotropin for early pregnancy outcomes. Arch Gynecol Obstet. 2020 Jan;301(1):295-302. (see)
Ziolkowska K, Dydowicz P, Sobkowski M, Tobola-Wrobel K, Wysocka E, Pietryga M. The clinical usefulness of biochemical (free β-hCg, PaPP-a) and ultrasound (nuchal translucency) parameters in prenatal screening of trisomy 21 in the first trimester of pregnancy. Ginekol Pol. 2019;90(3):161-166. (see)
FAQs from users: 'Why do I have hCG hormone in my blood if I am not pregnant?', 'What is the hCG pregnancy hormone used for?', 'What are the causes of elevated hCG in the blood?', 'What is the mechanism of action of hCG?', 'Can hCG be administered during lactation?' and 'Which medicine contains hCG hormone?'.
Authors and contributors
More information about Cristina Algarra Goosman
Hello, I am wondering what is the concentration of hormone the test can detect. If it´s too low I may get a negative even though I am pregnant right?
Hello Jenelle,
Yes, you can indeed get a negative pregnancy test if the concentration of hCG hormone is too low. Therefore testing at the correct time is essential to get a viable test result. At-home pregnancy test usually detects a minimum of 10mu/mL or 25 mu/mL, depending on the brand. The first ones having a lower threshold would detect pregnancy sooner.
I hope I could help,
All the best
Hello, I am 10DPO and took an at-home pregnancy test, I am not sure if I am seeing the result correctly but it seems to be a very faint line, does that mean that I am pregnant?
Hello MaryAnn,
At-home pregnancy tests detect the concentration of hCG, this hormone starts to produce once the embryo is implanted in the womb. This whole process from fertilization to implantation takes about two weeks, typically the time you would expect your period to come.
We recommend you wait after a missed period to test. If you have obtained a faint line 10dpo it could indicate you are pregnant. hCG values double every 24-48h. Therefore, if the test is indeed positive if you retake it a couple of days after you will see the line get darker.
I hope I could help,
All the best