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Blood test for hCG during pregnancy: interpretation of the results
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One of the most important laboratory studies in obstetrics is the analysis of hCG during pregnancy or the determination of a human chorionic gonadotropin in the blood.
It is a positive analysis of hCG in the early stages of pregnancy is an unconditional indicator of the successful fertilization of the ovum, the formation of the zygote, and then the blastocyst - with the introduction of the trophoblast into the endothelium of the uterus and the beginning of embryo development.
HCG - what is it?
HCG is a gonadotroph, a biologically active heterodimeric glycoprotein compound of more than two hundred amino acids, that is, a hormone that provides certain biochemical processes during pregnancy. In the composition of hCG two subunits - alpha and beta. The alpha subunit consisting of 92 amino acids is considered identical to such hormones as luteinizing (LH), follicle stimulating (FSH) and thyrotropic (TSH). And with the free beta subunit of chorionic gonadotropin (beta-hCG) consists of 145 amino acids and determines the unique properties of this hormone.
It is called chorionic because it is produced by the temporary organ of the embryo - its villous shell - by the chorion. The process of formation of the chorion from the trophoblast cells and the extraembryonic mesoderm of the inner blastocyst leaf occurs immediately after its attachment to the uterine wall.
After about a week, cells of the trophoblast of the chorion begin to produce chorionic gonadotropin, which interacts with the LHCG receptors of the embryo and helps maintain the yellow body of the ovaries before the 8th week of gestation. This is a very important function of hCG during pregnancy, since before the formation and beginning of the functioning of the placenta, another gonadotropic hormone is synthesized by the yellow body - progesterone, supporting pregnancy by suppression of ovulation, stimulating transformation of the endometrium and the formation of a network of capillaries.
In addition, due to its negative charge, hCG removes the immune cells of the mother from the embryo, preventing rejection of the fetus in the first trimester. Also, this hormone plays a role in the proliferation of embryonic cells. After their differentiation into types of tissues and complete formation of the placenta (during the fourth month of pregnancy), the synthesis of hCG takes on the placenta.
In 85% of pregnant women, the hCG level in the blood doubles every 48-72 hours in the first four weeks of pregnancy. The hormone is first found in the blood, and then in the urine.
When it is possible to do hCG analysis on pregnancy, and when the test for hCG shows pregnancy? It is possible to take an analysis of hCG in the early stages of pregnancy 12 days after the delay of the next monthly. A blood test will show the pregnancy 10-11 days after conception, and on the 12-14th day the hormone can be detected in the urine.
Although the levels of hCG in urine are usually lower than in serum, the excretion of the hormone by the kidneys is used in fast test strips. Answering the question, what is more reliable - an analysis of HCG or a pregnancy test? - Obstetricians-gynecologists emphasize the higher sensitivity of hCG analysis in the blood. This means that when examining a blood sample, you can establish the fact of pregnancy several days earlier than using a test.
In addition, if a woman's pregnancy test is used a short time after the alleged conception, when the level of hCG, including urine, is not high enough, a false negative result is obtained. See also - Pregnancy test at home
Indications for the procedure HCG during pregnancy
First of all, the analysis of hCG during pregnancy is taken to confirm the fact of pregnancy.
Also, this analysis allows monitoring of the course of pregnancy, especially in diabetes and gestosis in pregnant women; to establish a frozen (undeveloped) pregnancy; early diagnosis of ectopic (ectopic) pregnancy; in time to identify and prevent the threat of arbitrary termination of pregnancy (habitual miscarriage); to determine the insufficiency of the placenta.
To detect genetic abnormalities of the embryo (Patau, Down's syndrome, Edwards, Turner, Klinefelter-Albright) and delayed fetal development, prenatal pregnancy screening is performed using blood tests for beta-hCG at 9-12 and 16-18 weeks.
The rules for taking an HCG pregnancy test are simple, and the whole preparation for it is that the last meal should be 6-8 hours before taking blood from the vein; three days before the procedure should limit the intake of protein of animal origin and physical activity, as well as not take any medication. The delivery of blood is prescribed for the morning hours - on an empty stomach.
The technique completely corresponds to the method of taking blood from the peripheral vein by means of disposable sterile closed systems (syringe-tube with a needle).
How much is the hCG used in pregnancy? Blood is taken within 10-15 minutes, and decoding, as a rule, is ready in two or three days.
Absolute indicators of the level of chorionic gonadotropin in the blood are absent in pregnancy, but for each term there is a certain range of its content, which ensures normal fetal bearing.
In this case, it is necessary to take into account the presence of different units of measuring the level of hCG in the blood plasma (mIU / ml, mU / ml or ng / ml), which causes differences in the results and accepted standards of analysis, causing many questions in pregnant women.
It is considered normal to analyze hCG in early pregnancy with the following indicators: 1- 2 weeks - 25-300 mIU / ml (mU / ml), 2-3 weeks -1500-4900. At the same time, it can be considered normal at an early stage to increase hCG by 35% for every 48 hours or 50% - every 72 hours.
The accepted norm of the analysis of hCG during pregnancy on weeks from the moment of conception (in mIU / ml) is:
- at a period of 3-4 weeks - 1110-31500;
- 4-5 weeks - 2600-82400;
- 5-6 weeks - 23000 -150000;
- 6-7 weeks - 27000 - 233000;
- 9-12 weeks - 25700- 290000;
- 13-16 weeks - 6170-253000:
- 17-24 weeks - 4700-165000;
- 25 weeks and further - from 3640 to 117 000.
For the period of 11-13 weeks, the average statistical value in the range of 50 000-55 000 mIU / ml was taken as the norm. Also, the average indices for weeks (from 14th to 21st) are given in the publication - Chorionic gonadotropin in the blood
Interpretation of hCG analysis in pregnancy
The level of HCG below 5 mIU / ml is considered negative; a positive indicator, that is, when a woman becomes pregnant, is 25 mIU / ml and higher. If the result shows 6-24 mIU / ml, then a second test (7-10 days) is required to confirm the pregnancy.
What should be the analysis of hCG during pregnancy? As mentioned above, the level of this hormone is in the dynamics and constantly rises, reaching peak values for a period of 9-12 weeks, then it begins to gradually decrease, after 20 weeks the level stabilizes, but the hormone continues to be produced by the placenta until the end of gestation.
HCG should not be detected either in the blood or in the urine a week after delivery. The norm of HCG in non-pregnant patients is 0-5 mIU / ml; For postmenopausal women, the level of hCG up to 14 mIU / ml can be considered normal.
It is important to monitor the rise and fall of hCG levels. A blood test for hCG in ectopic pregnancy is performed weekly to determine the level of the hormone in the dynamics, which turns out to be less pronounced than in normal pregnancy. Read more - Ectopic pregnancy
Significant reduction in the content of this hormone in the blood is noted in cases of threat of miscarriage and the delay in fetal development, a rapid decrease in the results shows an analysis of hCG in a frozen pregnancy and in cases where the fetus dies on terms after 9-12 weeks. More information in the article - How to determine a frozen pregnancy?
The increase in the level is possible due to the development of multiple pregnancy, with genetically determined fetal anomalies, diabetes mellitus and gestosis in pregnant women. Also, the level of hCG may appear above the norm when patients are mistaken with the terms of conception. But based on the level of human chorionic gonadotropin in the blood, a doctor can correctly assess the gestational age of the fetus.
Prenatal diagnosis of congenital diseases is performed for the detection of intrauterine chromosome defects in the future child : ultrasound, protein-A analysis of blood plasma (PAPP-A), free estriol level assay, inhibin-A-derived gonadotropin levels, and hCG and AFP during pregnancy (at a period of 14-25 weeks). What is an ACE and for what is its analysis done, for more details see - Analysis of alpha-fetoprotein in pregnancy
Normal growth of hCG is an indicator of a viable pregnancy. According to obstetricians, the timely analysis of hCG during pregnancy is important, because the sooner a woman learns that she is pregnant, the faster she can change any habits that can harm her and her future child.