Free p-subunit of chorionic gonadotropin in serum
HC 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. HC is detected in the serum of the 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 CG is to stimulate the synthesis of progesterone by the yellow body in the early stages of pregnancy, it is also believed that HG 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 HG molecules, free a- and b-subunits can circulate in smaller amounts in the peripheral blood. The active synthesis of HG continues until the 9th to 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( Table).
Table Concentration of HG in serum in the dynamics of physiological pregnancy
Table Concentration of HG in serum in the dynamics of physiological pregnancy
In the first trimester, the ratio of free p-HG and CG is 1-4%, and in the II and III trimester - less than 1%.In the presence of chromosomal aberrations in the fetus, the level of free p-CG increases more rapidly than the concentration of total CG, so the determination of p-CG is preferable to prenatal screening in the first trimester of pregnancy( optimally at the 9-11th week).The median values of serum p-HG concentration for screening of congenital malformations in the first and second trimester of pregnancy are given in Table 1.
Table Median values of b-HG serum concentrations for screening of congenital malformations in the first and second trimester of pregnancy
Table Valuesmedian serum b-CG concentration for screening of congenital malformations in the first and second trimester of pregnancy
When evaluating the results of the study, it should be noted that a number of drugs( synthetic gestagens) are widely usedfor the treatment of miscarriage, activate the synthesis of p-CG.In case of multiple pregnancies, the content of p-CG in the blood increases in proportion to the number of fetuses.