The hormone hCG (human chorionic gonadotropin) is also referred to as “pregnancy-preserving hormone.” It stimulates the production of the pregnancy hormone progesterone, without which the pregnancy could not persist.
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What is hCG?
The pregnancy-preserving hormone is formed in the outer cell layers of the fertilized egg from the fifth day after fertilization. His most important task is to get the production of progesterone going.
At the beginning of pregnancy, progesterone ensures that the lining of the uterus is prepared to receive the fertilized egg. In combination with other hormones, it prevents the lining of the uterus from being rejected at the end of the cycle and prevents further monthly cycles during pregnancy.
The rapid increase in the first trimester of pregnancy
Normal blood hCG levels in non-pregnant women of childbearing age are less than 2 IU / liter (IU – international unit – a unit commonly used in medicine). Four to five days after implantation of the fertilized egg in the lining of the uterus (Nidation), the concentration of the pregnancy-sustaining hormone in the mother’s blood increases rapidly.
In the first two weeks after conception – i.e., in the 3rd and 4th week of pregnancy – it doubles every other day at least every other day, every three days after that, and every 5th day from the 7th week of pregnancy. Your maximum reaches it – with large individual fluctuation ranges – in the second half of the first trimester of pregnancy and amounts to between 11,000 and 289,000 IU / liter in the 7th to the 12th week of pregnancy.
After the end of pregnancy, the hCG concentration then decreases continuously until it reaches its initial level one to two weeks after birth.
hCG, progesterone and the role of the yellow body in early pregnancy
At the beginning of pregnancy, the pregnancy-preserving hormone is formed directly by the fertilized egg cell; later its production is taken over by the placenta with the help of the outer eggshell – the chorion. About five days after conception – just before nidation – trophoblast cells begin to produce hCG, which stimulates the release of progesterone in the corpus luteum.
The yellow body (corpus luteum) is formed during ovulation. It consists of the cells of the follicular skin that remain after the mature ovum has left the follicle through ovulation. Immediately afterward, the corpus luteum begins to produce progesterone as well as female sex hormones (estrogens).
However, progesterone levels sufficient to maintain pregnancy are only formed under the influence of pregnancy-sustaining hormone. It also helps maintain the yellow body – the hormone increases in size and at the end of the first trimester of pregnancy, it fills up about half of the ovary where the egg matured for that pregnancy.
Until the 4th month of pregnancy, the corpus luteum is the main supplier of progesterone. After that, this task takes over the placenta, which produces the hormone until birth in much larger quantities. The task of pregnancy-preserving hormone is thus fulfilled – its production can now be reduced.
What diagnostic information does the hCG value provide?
The detection of human chorionic gonadotropin in the blood is solid evidence that it is pregnant – the doctor can take this test about seven days after conception. The commercial pregnancy tests, on the other hand, measure the significantly low hCG concentration in the mother’s urine, but they only deliver a reliable result from the 5th week of pregnancy.
Very high concentrations of the hormone can be caused by a multiple pregnancy, but also embryonic aberrations such as moles or degeneration of the chorion.
Very low levels may be indicative of a non-viable embryo or extrauterine pregnancy ( tubal or buccal cavity pregnancy ). At the initial examination and further check-ups in early pregnancy, therefore, the hCG value is always examined.
Human chorionic gonadotropin in first-trimester screening and fertility medicine
As part of the so-called first-trimester screening, the child’s nuchal translucency as well as various maternal blood values – including the concentration of free beta-hCG – are measured. Based on this data, the physician calculates the statistical probability that the baby suffers from trisomy 21 (Down syndrome) or some other genetic defect. For example, in trisomy-21 children, the beta-hCG level in the mother’s blood is usually much higher than that of other children.
Also, hCG is also used in fertility medicine. A yellow body weakness is often the reason that no pregnancy occurs or affected women lose their child through a very early miscarriage – injections of the pregnancy-preserving hormone to stimulate both the growth of the corpus luteum and its hormone production in such cases.
- The hormone hCG (human chorionic gonadotropin) is responsible for the maintenance of pregnancy
- It stimulates the production of progesterone in the corpus luteum and ensures that it can fulfill its function as a progesterone supplier until the 4th month of pregnancy
- In early pregnancy, the hCG value performs various diagnostic functions
- Also, the pregnancy-preserving hormone is used in fertility medicine