Blood test for hCG in pregnancy: deciphering the results

One of the most important laboratory tests in obstetrics is the analysis of hCG during pregnancy or the determination of human chorionic gonadotropin in a woman’s blood.

It is a positive hCG test in the early stages of pregnancy that is an absolute indicator of successful fertilization of the egg, the formation of a zygote, and then a blastocyst - with the introduction of its trophoblast into the endothelium of the uterus and the beginning of the development of the embryo.

HCG - what is it?

HCG is a gonadotropin, a biologically active heterodimeric glycoprotein compound of more than two hundred amino acids, i.e. a hormone that ensures certain biochemical processes during pregnancy. HCG consists of 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 thyroid-stimulating (TSH). And the free beta subunit of human 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 membrane - the chorion. The process of formation of the chorion from trophoblast cells and extraembryonic mesoderm of the inner layer of the blastocyst occurs immediately after its attachment to the wall of the uterus.

After about a week, the chorionic trophoblast cells begin to produce human chorionic gonadotropin, which interacts with the LHCG receptors of the embryo and helps maintain the corpus luteum of the ovaries until the 8th week of gestation. This is a very important function of hCG during pregnancy, since before the formation and functioning of the placenta, the corpus luteum synthesizes another gonadotropic hormone - progesterone, which maintains pregnancy by suppressing ovulation, stimulating the transformation of the endometrium and the formation of a network of capillaries.

In addition, due to its negative charge, hCG diverts the mother's immune cells from the embryo, preventing rejection of the fetus in the first trimester. This hormone also plays a certain role in the proliferation of embryonic cells. After their differentiation into tissue types and the complete formation of the placenta (during the fourth month of pregnancy), the placenta takes over the synthesis of hCG.

In 85% of pregnant women, the level of hCG in the blood doubles every 48-72 hours during the first four weeks of pregnancy. The hormone is first detected in the blood and then in the urine.

When can you do an hCG pregnancy test, and when will the hCG test show pregnancy? You can take an hCG test in the early stages of pregnancy 12 days after the delay of your next period. A blood test will show pregnancy 10-11 days after conception, and on the 12th-14th day the hormone can be detected in the urine.

Although hCG levels in urine are usually lower than in serum, renal excretion of the hormone is used in rapid test strips. When answering the question, which is more reliable – hCG analysis or pregnancy test? – obstetricians and gynecologists emphasize the higher sensitivity of hCG analysis in blood. This means that when examining a blood sample, it is possible to establish the fact of pregnancy several days earlier than using a test.

In addition, if a woman uses a pregnancy test shortly after the expected conception, when the hCG level, including in urine, is not high enough, then a false negative result is obtained. See also - Home pregnancy test

Indications for the procedure HCG in pregnancy

First of all, the hCG test during pregnancy is taken to confirm the fact of pregnancy.

This analysis also allows monitoring the course of pregnancy, especially in cases of diabetes mellitus and gestosis in pregnant women; establishing a frozen (non-developing) pregnancy; diagnosing an ectopic (extrauterine) pregnancy in the early stages; promptly identifying and preventing the threat of spontaneous termination of pregnancy (habitual miscarriage); determining placental insufficiency.

To identify genetic abnormalities of the embryo (Patau, Down, Edwards, Turner, Klinefelter-Albright syndromes) and fetal growth retardation, prenatal screening of pregnancy is performed using blood tests for beta-hCG at 9-12 and 16-18 weeks.

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Preparation

The rules for taking the hCG pregnancy test are simple, and all preparation for it comes down to the fact that the last meal should be 6-8 hours before taking blood from a vein; three days before the procedure, you should limit the consumption of animal proteins and physical activity, and also not take any medications. Blood is scheduled for the morning hours - on an empty stomach.

The technique used is completely consistent with the method of taking blood from a peripheral vein using disposable sterile closed-type systems (syringe-test tube with needle).

How long does it take to do an hCG test during pregnancy? Blood is taken within 10-15 minutes, and the results are usually ready in two to three days.

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Normal performance

There are no absolute indicators of the level of human chorionic gonadotropin in the blood during pregnancy, but for each period there is a certain range of its content, which ensures normal gestation of the fetus.

It is important to take into account the presence of different units of measurement of the hCG level in blood plasma (mIU/ml, mIU/ml or ng/ml), which is why both the results and the accepted standards for the tests differ, causing many questions among pregnant women.

The hCG analysis is considered normal in the early stages of pregnancy with the following values: 1-2 weeks - 25-300 mIU/ml (mIU/ml), 2-3 weeks - 1500-4900. At the same time, an increase in hCG by 35% every 48 hours or by 50% every 72 hours can be considered normal in the early stages.

The accepted norm for hCG analysis during pregnancy by week from the moment of conception (in mIU/ml) is:

• at 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 beyond – from 3640 to 117,000.

For the period of 11-13 weeks, the average statistical indicator in the range of 50,000-55,000 mIU/ml is taken as the norm. Also, the average indicators by week (from the 14th to the 21st) are given in the publication - Human chorionic gonadotropin in the blood

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Interpretation of hCG test results during pregnancy

An hCG level below 5 mIU/ml is considered negative; a positive indicator, i.e. when a woman is pregnant, is 25 mIU/ml or higher. If the result shows 6-24 mIU/ml, then a repeat test (after 7-10 days) is required to confirm pregnancy.

What should be the hCG analysis during pregnancy? As noted above, the level of this hormone is dynamic and constantly increases, reaching peak values at 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 detectable in either blood or urine one week after delivery. The normal hCG level for non-pregnant women is 0-5 mIU/ml; for postmenopausal women, a normal hCG level can be up to 14 mIU/ml.

It is important to monitor the increase and decrease of hCG levels. Blood tests for hCG in ectopic pregnancy are performed weekly to determine the level of the hormone in dynamics, which is less pronounced than in normal pregnancy. More details - Ectopic pregnancy

A significant reduction in the content of this hormone in the blood is observed in cases of threatened miscarriage and intrauterine growth retardation, a rapid decrease in results is shown by the analysis of hCG in case of a frozen pregnancy and in cases where the fetus dies after 9-12 weeks. More information in the article - How to determine a frozen pregnancy?

An increase in the level is possible due to the development of multiple pregnancies, with genetically determined fetal abnormalities, with diabetes mellitus and gestosis in the pregnant woman. Also, the hCG level may look abnormal when patients are mistaken about the timing of conception. But based on the level of human chorionic gonadotropin in the blood, the doctor can correctly estimate the gestational age of the fetus.

To detect intrauterine chromosomal defects in the future child, prenatal diagnostics of congenital diseases is carried out: ultrasound, analysis of plasma protein-A (PAPP-A), analysis of the level of free estriol, the content of the gonadotropin inhibin-A produced by the placenta, as well as hCG and AFP tests during pregnancy (at 14-25 weeks). For more details on what ACE is and why its analysis is done, see - Alpha-fetoprotein analysis during pregnancy

Normal growth of hCG is an indicator of a viable pregnancy. According to obstetricians, timely hCG analysis during pregnancy is important, because the sooner a woman finds out that she is pregnant, the faster she can change any habits that can harm her and her future child.