Free beta subunit of the chorionic gonadotropin

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. Chorionic gonadotropin is detected in the serum of a pregnant woman on the 8th-12th day after fertilization. Its concentration is rapidly increasing during the first trimester, doubling every 2-3 days. The maximum concentration is 8-10 weeks, after it begins to decline and during the second half of pregnancy remains more or less stable.

The physiological role of chorionic gonadotropin is to stimulate the synthesis of progesterone by a yellow body in the early stages of pregnancy, it is also believed that the chorionic gonadotropin stimulates the synthesis of testosterone by the male reproductive glands of the fetus and affects the adrenal cortex of the embryo.

In addition to whole molecules of the chorionic gonadotropin, free alpha and beta subunits can circulate in a smaller amount in the peripheral blood. The active synthesis of chorionic gonadotropin continues until the 9th-10th week of pregnancy (the time of the final formation of the placenta). Further, the concentration of the hormone in the blood and, accordingly, in the urine decreases and remains constant until the end of pregnancy.

Concentration of chorionic gonadotropin in serum in the dynamics of physiological pregnancy

Pregnancy, ned	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 and chorionic gonadotropin is 1-4%, and in the second and third trimester - less than 1%. In the presence of chromosomal aberrations in the fetus, the level of free beta-chorionic gonadotropin rises faster than the concentration of the common chorionic gonadotropin, therefore, the determination of beta-chorionic gonadotropin is preferable to prenatal screening in the first trimester of pregnancy (optimally at week 9-11).

Median concentrations of β-chorionic gonadotropin in serum for screening of congenital malformations in the first and second trimester of pregnancy

Pregnancy, ned	Median concentrations of β-chorionic gonadotropin, ng / ml
10	41.5
Eleven	34.6
12	32.7
13	28.7
15	14.1
16	11.0
17th	10.5
18	9.4
19	6.8
20	4.7

When evaluating the results of the study, it should be borne in mind that a number of drugs (synthetic gestagens) widely used for the treatment of miscarriage, activate the synthesis of beta-chorionic gonadotropin. In multiple pregnancies, the content of beta-chorionic gonadotropin in the blood increases in proportion to the number of fruits.

[1], [2], [3], [4], [5], [6], [7]