Medical expert of the article
New publications
Free beta-subunit of chorionic gonadotropin
Last reviewed: 05.07.2025
All iLive content is medically reviewed or fact checked to ensure as much factual accuracy as possible.
We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies. Note that the numbers in parentheses ([1], [2], etc.) are clickable links to these studies.
If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please select it and press Ctrl + Enter.
Human chorionic gonadotropin is a glycoprotein with a molecular weight of approximately 46,000, consisting of two subunits - alpha and beta. The protein is secreted by trophoblast cells. Human chorionic gonadotropin is detected in the blood serum of a pregnant woman on the 8th-12th day after fertilization. Its concentration increases rapidly during the first trimester, doubling every 2-3 days. The maximum concentration occurs at 8-10 weeks, after which it begins to decrease and remains more or less stable during the second half of pregnancy.
The physiological role of human chorionic gonadotropin is to stimulate the synthesis of progesterone by the corpus luteum in the early stages of pregnancy; it is also believed that human chorionic gonadotropin stimulates the synthesis of testosterone by the male gonads of the fetus and affects the adrenal cortex of the embryo.
In addition to whole molecules of chorionic gonadotropin, free alpha and beta subunits may circulate in smaller quantities in the peripheral blood. Active synthesis of chorionic gonadotropin continues until the 9th-10th week of pregnancy (the time of final formation of the placenta). Subsequently, the concentration of the hormone in the blood and, accordingly, in the urine decreases and remains constant until the end of pregnancy.
Serum chorionic gonadotropin concentration in the dynamics of physiological pregnancy
Gestational age, weeks |
Median, IU/L |
Reference values, IU/L |
1-2 |
150 |
50-300 |
3-4 |
2,000 |
1,500-5,000 |
4-5 |
20,000 |
10,000-30,000 |
5-6 |
50,000 |
20,000-100,000 |
6-7 |
100,000 |
50,000-200,000 |
7-8 |
70,000 |
20,000-200,000 |
8-9 |
65,000 |
20,000-100,000 |
9-10 |
60,000 |
20,000-95,000 |
10-11 |
55,000 |
20,000-95,000 |
11-12 |
45,000 |
20,000-90,000 |
13-14 |
35,000 |
15,000-60,000 |
15-25 |
22,000 |
10,000-35,000 |
26-37 |
28,000 |
10,000-60,000 |
In the first trimester, the ratio of free beta-chorionic gonadotropin to human chorionic gonadotropin is 1-4%, and in the second and third trimesters - less than 1%. In the presence of chromosomal aberrations in the fetus, the level of free beta-chorionic gonadotropin increases faster than the concentration of total chorionic gonadotropin, therefore, the determination of beta-chorionic gonadotropin is preferable for prenatal screening in the first trimester of pregnancy (optimally at 9-11 weeks).
Values of median concentrations of β-human chorionic gonadotropin in blood serum for screening of congenital malformations in the first and second trimesters of pregnancy
Gestational age, weeks |
Median concentration of β-human chorionic gonadotropin, ng/ml |
10 |
41.5 |
11 |
34.6 |
12 |
32.7 |
13 |
28.7 |
15 |
14.1 |
16 |
11.0 |
17 |
10.5 |
18 |
9.4 |
19 |
6.8 |
20 |
4.7 |
When evaluating the results of the study, it should be taken into account that a number of drugs (synthetic gestagens), widely used to treat miscarriage, activate the synthesis of beta-chorionic gonadotropin. In multiple pregnancies, the content of beta-chorionic gonadotropin in the blood increases proportionally to the number of fetuses.
[