Biochemical blood test screening 1 trimester transcript. prenatal screening. Preparation and conduct of screening

Biochemical screening of the 1st trimester: what kind of analysis is it, how is it done and why?

In the early stages, when registering pregnant women, they are sent for a mass of tests: KLA, OAM,.

But that is not all. One of the main studies in the first trimester is biochemical screening. What kind of analysis is this, how it is done, the preparation and interpretation of the result will be discussed in the article.

• What is screening
• What is prenatal screening and its purposes
• Prevention of malformations
• Preparation
• How to pass the analysis
• When will the results be ready
• Why do you need to do an ultrasound
• Timing of prenatal tests
• Pregnant at risk - what to do next
• False positive and false negative results
• How are the tests for chromosomal abnormalities calculated?
• Typical MoM profiles for the 1st trimester
• Typical MoM profiles for the 2nd trimester
• Factors affecting the concentration of biochemical markers
• conclusions

What is screening?

The concept of screening in medicine is widely used. This is a routine study aimed at identifying a risk group for a disease or pathology. There is screening for:

• breast cancer;
• tuberculosis;
• gastrointestinal tumors, etc.

Note! The result of the test is not a diagnosis, but the identification of a risk group.

Why do biochemical screening for pregnant women

During pregnancy, especially in the early stages, it is important to understand which way gestation will develop and whether the fetus will develop at all.

Biochemical screening of the 1st trimester, to some extent, determines the fate. The causes are genetic diseases, chromosomal abnormalities leading to malformations. And according to WHO, 5% of them worldwide. This is natural selection - non-viable fetuses are eliminated from the mother's body.

Nature is not always able to protect a woman from pregnancy with a fetus with genetic disorders. If chromosomal diseases incompatible with life are detected, the “doomed conception” is recommended to be interrupted. At the beginning of pregnancy, it is easier to do this and there are fewer complications for the mother's body. The second purpose of the triple test is to identify the risk of pregnancy complications. The third is to determine the group of pregnant women who will be recommended additional studies if fetal pathology is suspected.

The entire prenatal screening funnel looks like this:

Genetic abnormalities of the fetus can be in a pregnant woman of any age. But the older the woman, the higher the likelihood of their occurrence. This trend is most pronounced for Down syndrome. For other genetic diseases, it is less pronounced, but still present.

Prevention of malformations

In modern medicine, a clear plan has been developed for the prevention and timely detection of malformations. It is necessary to identify malformations incompatible with life and early planned termination of pregnancy.

Not all vices are related to vitality. There are developmental disorders that can be treated immediately after birth, and for some there is the possibility of intrauterine treatment. In such cases, timely assistance saves the lives of newborns. This is also important for situations where the baby needs help in the first hours or 1-2 days after birth. Such pregnant women should choose a maternity hospital in advance, in which they can perform life-saving surgery immediately after childbirth, for example, with aplasia of the esophagus.

Types of prevention:

• preconception;
• perinatal diagnosis.

Preconception prevention is a set of measures aimed at providing optimal conditions for:

• maturation of germ cells in men and women;
• fertilization;
• zygote formation;
• implantation and early fetal development.

This includes healthy family planning, reception, smoking cessation, etc.

When there are chromosomal diseases in the fetus, the concentration and ratio of these substances changes.

Chromosomal diseases are hereditary pathologies caused by changes in the number or structure of chromosomes. They appear during the maturation of germ cells, in the process of fertilization, at an early embryonic stage of development.

A blood test for fetal malformations by itself does not say anything. To decipher and interpret the results, ultrasound data are needed. Due to the fact that it is necessary to conduct 2 studies, biochemical screening is called a double test.

How to prepare for analysis

Special training is not required. A light breakfast, lunch or dinner is acceptable (depending on what time the woman will take the test). The main restriction is a strict ban on fatty foods. Foods with a high fat content will not change the results of the analysis, but will make it difficult for the laboratory technician to work. Since hormone proteins are not determined in the blood itself, but in the serum.

On the appointed day, the pregnant woman comes to the treatment room and, together with the specialist, fills out a detailed questionnaire.

Important! It is necessary to accurately fill out the questionnaire, the data from it is necessary to adjust the risks obtained during biochemical screening.

How the analysis is given - biochemical screening of the 1st trimester

After filling out the questionnaire, you need to weigh yourself. Height and weight must be recorded at the time of blood donation. These parameters are taken into account to adjust the calculated risks during the test.

Blood is taken from the vein of the elbow in a volume of 4-5 ml. Pour from the syringe into a test tube and centrifuge. And then they work not with blood, but with plasma.

How long will the result be

The timing of the analysis varies depending on the urgency. The result can be ready on the same day or within a week.

Why do ultrasound for biochemical screening

Among experts, biochemical screening is called a triple test, because not only hCG and PAPP-A values ​​\u200b\u200bare needed, but also results to determine genetic risks. Namely: the exact gestational age, the size of the TVP (thickness of the collar space of the fetus) and DNA (the length of the nasal bone of the fetus). DNA and TVP are ultrasound markers of malformations, in case of deviation from the norm. The rules for different periods are different.

It is important to know! If the nasal bone is not visualized, the risk of fetal pathologies rises to 47%.

Biochemical indicators and ultrasound markers are necessary for correct calculations of the risks of chromosomal diseases.

The thickness of the collar space is the area in the neck between the skin and soft tissues in which fluid accumulates. A pronounced excess of the norm may indicate abnormalities in the development of the fetus.

TVP norm. Table 1.

Ultrasound is highly accurate and is recommended by an expert class sonologist. The term of the first ultrasound is 11-14 weeks.

Important! The optimal time for an ultrasound as part of a triple test is -.

Prenatal biochemical screening and timing

In obstetrics, there are concepts: biochemical screening of the 1st trimester and biochemical screening of the 2nd trimester. It will not be possible to fully carry out prenatal diagnosis only in the second trimester, since the indicators obtained in the first trimester are involved in the calculations and decoding.

Biochemical screening in the 1st trimester is carried out in the period from 10 weeks of pregnancy to and 6 days. Optimal time - -.

Biochemical screening of the 2nd trimester is done at the term -. Optimal time - -.

A woman at risk - what to do next

The first screening serves to identify risk groups for chromosomal and non-chromosomal abnormalities. In the 1st trimester, risks are assessed for Down syndrome, Edwards, Patau and other genetic diseases that are less common. The risk of developing neural tube defects is not assessed (this occurs during biochemical screening conducted in the 2nd trimester).

The first analysis makes it possible to check the probability:

• development;

These complications of gestation are laid in the first 3-4 months, appear in the 3rd trimester, which allows for early prevention.

If a woman receives a biochemical screening result and the results show high risks for a particular disease, she is recommended to undergo fairly serious studies at prenatal diagnostic centers.

In perinatal centers, it may be necessary to repeat biochemical screening, ultrasound. After that, the question of conducting invasive diagnostics becomes. For a period of 11-13 weeks - this is a biopsy of the chorionic villi.

The chromosome set of the chorion corresponds to the set of the child's genetic material. During the biopsy, pieces of chorion tissue (the future placenta) are obtained for genetic analysis. The probability of error with invasive methods is low, they give an almost 100% accurate answer.

Initially, the tasks of biochemical screening in the 2nd trimester (quadruple test) are the same as in the 1st trimester.

This detection:

• chromosomal abnormalities;
• deviations not associated with genetic disorders that relate to the fetus itself and the course of gestation.

The diagnostic significance of the quadruple test is the definition of malformations. Recommended time frame - - . For biochemical screening of the 2nd trimester (fourth test), the following indicators are examined:

• alpha-fetoprotein AFP;
• free estriol;
• inhibin A.

In the second trimester, the fetus begins to synthesize its own proteins - ACE and estriol. Their number and ratio "characterize" its development.

The results of the 1st trimester screening are required for the second biochemical screening. For calculations, ultrasound data taken at 10-13 weeks are required. The significance of the thickness of the collar space and the length of the nasal bone of the fetus, determined after this period, disappears.

If risks are identified in the 2nd trimester, a woman is sent to a perinatal center, where the need for invasive diagnostics will be weighed:

• amniocentesis;
• cordocentesis.

The significance of amniocentesis and cordocentesis is approximately the same, the choice will depend on which technique is used in the hospital. The probability of complications in invasive diagnostics is 1-2%.

Can there be false positives and false negatives?

Reasons for false results may include:

• incorrectly determined terms of pregnancy;
• accounting results;
• non-compliance with the terms of ultrasound and analysis of biochemical screening;
• incorrect measurement of TVP.

The accuracy of the test is 93%.

The main stages of risk calculations during biochemical screenings

In the analytical laboratory, the following steps take place before the results are issued:

1. Determination of the concentration of analytes (determined substances).
2. Determination of the degree of deviation from the median for a certain gestational age - MoM.

1. Correction of IOM taking into account height, weight, ethnicity, concomitant diseases, results of the previous screening (2nd trimester).
2. Adjustment for age, body weight, risk factors (, bad habits).

Typical IOM profiles in the 1st trimester

What does an increased level of alpha-fetoprotein in the 1st and 2nd trimesters mean?

Typical IOM profiles in the 2nd trimester

Factors affecting the level of a biochemical marker

The decrease in biochemical markers is affected by:

• gestational age (the concentration of analytes varies depending on the period);
• weight (the greater the body weight, the lower the concentration of hormones in the blood);
• ethnicity (levels vary by race);
• twin pregnancy: the concentration of markers is increased, sometimes by 2 times;
• insulin-dependent diabetes mellitus (levels are reduced);
• smoking (hCG levels decrease by 18%);
• pathology of the placenta and its location;
• features of the course of pregnancy;
• pregnancy.

conclusions

Biochemical screenings are important studies required for all pregnant women. They allow you to determine the risks of fetal pathologies and the course of pregnancy, which makes it possible to correct adverse situations for the health of the expectant mother and baby. Most women get good results, which inspires confidence in a happy and healthy future for the child.

Actual video

Prenatal screening

Every pregnant woman in the first trimester should undergo an examination such as screening. It is necessary in order to determine the risks of abnormalities in the development of the fetus at the earliest stages. In medicine, average test results are established, which indicate that the health of the unborn baby is normal. However, some deviations are permissible, since they can be influenced by the characteristics of each woman. Therefore, having made a screening of the 1st trimester, you need to contact your doctor to decipher the results and prescribe other necessary tests.

How is first trimester screening done?

Screening of the 1st trimester is carried out in the period from 11 to 13 weeks of pregnancy, less often at 9-10 weeks, in 2 stages. For its full implementation, it is necessary to undergo an ultrasound examination and take a blood test. In addition, other survey results are taken into account. Currently, most laboratories use a special computer program that, based on all the data provided, produces a result. The result contains the level of risk of having a baby with such serious deviations as Down and Edwards syndromes. But different laboratories use different equipment and calculation systems, therefore, to obtain reliable results, it is necessary to pass all the tests in one place.

Ultrasound screening is a traditional examination of the fetus. It is produced either through the skin of the abdomen or through the vagina. As a rule, the method is determined by the position of the fetus - preference is given to the one in which the required area will be best viewed.

Along with an ultrasound examination, a blood test is performed for the level of various elements. It is called biochemical screening. As a result, the level of hCG (human chorionic gonadotropin) is detected.

Screening Norms

When screening of the 1st trimester is carried out, the norm is determined differently in each case. It also depends on the methods used by a particular laboratory, and on the characteristics of the female body. In any case, you should trust specialists in this matter, since it is extremely difficult to determine on your own how dangerous the situation is. Even in case of deviations from the norm, the doctor does not make a specific diagnosis, but prescribes additional examinations.

Keeping in mind the ultrasound screening of the 1st trimester, the norm is set depending on several indicators. The thickness of the collar space (abbreviated TVP) is measured. If it exceeds the norm, then the risk of developing Down syndrome is high. In this case, it is necessary to pay attention to other points, such as the presence of the nasal ossicle, the size of the maxillary ossicle, the size of the bladder, the number of umbilical arteries, the appearance of venous blood flow and the heart rate.

In a biochemical study, a blood test is performed. As a result, the level of hCG or the free β-subunit of hCG and PAPP-A is detected (this is an English abbreviation, the decoding of which can be translated into Russian as “plasma protein A associated with pregnancy”).

Averages

When a pregnant woman undergoes biochemical screening of the 1st trimester, the norm can be determined in different ways, but the following indicators are most often used.

Free β-subunit of hCG:

• 9 weeks: 23.6 - 193.1 ng / ml;
• 10 weeks: 25.8 - 181.6 ng / ml;
• 11 weeks: 17.4 - 130.4 ng / ml;
• Week 12: 13.4 - 128.5 ng / ml;
• Week 13: 14.2 - 114.7 ng / ml.
• PAPP-A level norm:
• 8-9 weeks: 0.17 - 1.54 mU / ml;
• 9-10 weeks: 0.32 - 2.42 mU / ml;
• 10-11 weeks: 0.46 - 3.73 mU / ml;
• 11-12 weeks: 0.79 - 4.76 mU / ml;
• 12-13 weeks: 1.03 - 6.01 mU / ml;
• 13-14 weeks: 1.47 - 8.54 mU / ml.

There is also a common indicator for all, it is a coefficient value, which is obtained as a result of a study of the ratios of various substances in the blood. It is denoted by the English abbreviation MoM, it stands for approximately as a multiple of the average. In an ideal situation, it is equal to one. But these are extremely rare, and readings ranging from 0.5 to 2 MoM are considered the norm.

Possible causes of deviations from the norm

What should you do if you find abnormalities in your tests as a result of screening? First, you shouldn't worry. Naturally, you need to immediately make an appointment with a doctor. The fact is that researching the condition of a pregnant woman and a growing baby is a very complex process that only specialists can do. Each person is unique, he has his own characteristics and diseases. All this affects the results of the analysis. Therefore, before drawing concrete conclusions, it is necessary to undergo additional examination.

Often deviations from the norm can be caused by the following reasons:

• smoking;
• taking certain medications;
• diabetes;
• feeling unwell during the test;
• pregnancy as a result of artificial insemination;
• multiple pregnancy;
• low or overweight women;
• severe pregnancy, the threat of miscarriage.

Screening of the 1st trimester is a necessary examination that allows you to identify violations at the earliest stages and take the necessary measures. These tests are safe for the health of the unborn baby and the pregnant woman, so you need to go through them. When examining the results, trust the doctor. But if immediately after biochemical screening he insists on terminating the pregnancy, talking about serious deviations, keep in mind that such conclusions are premature, and you need to take additional tests. This will help confirm or refute concerns and take action.

For many girls, just the phrase about screening the first trimester already causes excitement.

Meanwhile, prenatal fetal screening implies an absolutely painless comprehensive examination.

When they spend

The first is carried out initially in the 1st trimester of pregnancy, that is, on -.

Screening of the first trimester allows you to determine the likelihood of having a baby with congenital malformations of its development (CMD).

What it is

Prenatal ultrasound screening of the fetus is a set of specific diagnostic measures for a pregnant woman.

Screening methods are called studies that can be used for a large-scale survey, because they are safe and easy to perform.

The results show possible gross anomalies in the development of the fetus and indirect signs of pathologies.

Perinatal fetal screening includes:

1. Special ultrasound screening
   • traditional ultrasound examination (everyone usually calls it) of the fetus throughout pregnancy. How this procedure is carried out, you can see in the photo and video.
   • If you are interested in how much it costs, then know that in each clinic the prices for ultrasound are different. For example, in Invitro, a study costs about 1,500 rubles.
2. Biochemical screening.
   • It is aimed directly at identifying the risks of developing syndromes such as Edwards or Down syndrome.

The study involves the determination of certain specific substances in the blood (the so-called "markers") - they always change in the presence of certain pathologies.

Fetal biochemistry during the first trimester does not make it possible to make an accurate diagnosis.

The results of the survey only to some extent allow us to identify women with a slightly high risk of any pathology.

And in order to make a more accurate diagnosis, it is necessary to conduct additional examinations (invasive diagnostics, ultrasound).

What is examined in the first trimester

Biochemical analysis involves donating blood, which is examined in the laboratory for the presence of β-hCG - the so-called human chorionic hormone.

Also in the blood, plasma protein A (denoted by PAPP) associated directly with pregnancy, and AFP (decoding alpha-fetoprotein) are examined.

The results of the 1st trimester screening are usually sent to the attending physician from the laboratory, and he is already evaluating the data received.

Based on whether a poor analysis, or the results are normal, the doctor gives the pregnant woman further recommendations. Refers to a combined or assigns a more detailed diagnosis to a woman.

When calculating the risk of pathology, or vice versa, the norms find out the weight, age, possible hereditary ailments of a pregnant woman, mother's illness, her bad habits. Results (indicators) also depend on all this.

The results and norms of research are evaluated in modern laboratories, using an automated special program called Prisca. What it is?

Prisca is a computer program. It is Priska who evaluates, in accordance with the results of the analysis, the individual probability of various chromosomal diseases, as well as other possible congenital anomalies of the unborn child.

The optimal time for screening is 11-13 weeks of pregnancy.

Biochemical screening of the fetus during the first trimester of pregnancy (the so-called "double test") includes the following studies:

• Free b-subunit of human chorionic gonadotropin (or simply free β-hCG).
• The plasma protein A that is associated with pregnancy is PAPP-A.

However, in order to calculate the risk of trisomy and determine the norms using the Prisca program, ultrasound results are needed.

That is, in order to determine the indicators of the norm and risks, the doctor will definitely need ultrasound data, which was carried out in the 1st trimester, namely, KTP (coccygeal-parietal size) or ultrasound KTP + TVP (survey results (video / photo) with the thickness of the collar space) .

Indications for biochemical analysis

This examination during the first trimester is necessarily done with such indications:

• When a woman has her first pregnancy after 30 years.
• If you have had several miscarriages before.
• If the expectant mother has hereditary pathologies.
• If a woman already has children with some kind of genetic type pathologies.
• When deviations from the norm / risks are found during the ultrasound of the first trimester.
• With severe pathologies during pregnancy, which confirmed the results of ultrasound.
• If a woman works in a hazardous industry.
• If the marriage is closely related.
• If at the beginning of pregnancy a woman has been ill with viral diseases.

Tests for diseases that are directly transmitted sexually are also carried out in the 1st trimester, since they can cause very serious pathologies during the further development of the fetus.

A blood test allows you to:

• detect signs/presence of rubella, as well as viral hepatitis B.
• assess the level of certain hormones of a woman during pregnancy.
• a thorough study of the total level of glucose in the blood during the entire period of pregnancy allows the doctor to monitor certain blood parameters that are responsible for gestational diabetes mellitus and prescribe treatment in time.

In turn, an elevated protein level in the blood may indicate the presence of any pathology of the urinary system, kidneys, and even the development of preeclampsia.

How many of these tests you need to take, the attending physician determines, depending on what results the first analysis gave.

Deciphering the norm

1. The norms of pregnancy-associated plasma protein A are from 0.46 to 8.54 MIU / ml. If the analysis gave a result below the norm, this indicates a threat of miscarriage, Down syndrome, as well as Edwards syndrome.
2. Analysis for the beta subunit of human gonadotropin (chorionic). Normal - 20000 - 60000 IU / l.

A bad result is any deviation from the norm.

Every expectant mother from the moment of conception of a child begins to tune in to a lot of tests, analyzes and medical consultations. As frightening as all this may be for pregnant women, without such studies it is not possible to reveal the likely serious risks associated with the health of the fetus. Throughout the entire period, it is necessary to adhere to the entire prevention program, which is prescribed by the attending gynecologist.

It is important not to neglect the recommended analyzes. Biochemical screening is considered one of the most mandatory tests. Despite the unattractive name, this analysis is very useful for building a picture of the health of the unborn child.

What it is

Biochemical blood screening is a rather narrow-profile analysis. Refers to the initial and additional categories of tests. Detects signs of diseases such as hepatitis B and rubella. In the extended version, the analysis allows you to determine the presence of syphilis and HIV infection in the blood.

Nevertheless, the main function of screening is to identify the predisposition of the fetus to pathologies. Also, the results of the analysis clearly demonstrate how certain diseases will develop in the embryo in the future. In this regard, the attending physician builds a phased program for the treatment or prevention of pathologies.

Biochemical screening allows you to determine the Rh factor and blood type. These characteristics will be extremely useful in the future if the mother needs proper treatment. For the appointment of serious hormonal drugs, it is important to know the Rh factor of the pregnant woman and her offspring.

Screening at later dates allows you to identify the likelihood of the so-called gestational diabetes.

Who is shown the procedure

Every pregnant woman should undergo biochemical screening. Some experts question the urgent need for analysis. However, hardly anyone can guarantee that none of the expectant mothers has serious genetic disorders. The fact is that many women are unaware of a pathological failure in their body, as well as infections. Some mothers have a hereditary predisposition to genetic diseases that can be passed down through generations.

On the territory of Russia, such a biochemical test is one of the mandatory tests during the second trimester. However, it is performed on a voluntary basis. Doctors recommend analysis as an additional insurance to obtain information about the condition of the mother and her child.

Possible risks

Any procedure for interfering with the current work of the body carries certain dangers. In reality, the risks of medical tests are minimized.

The first screening slightly increases the chance of fetal loss. This is the biggest risk associated with this type of analysis. Standard screening will not harm the fetus in any way. However, its perinatal varieties, such as chorionic biopsy and amniocentesis, can greatly aggravate the course of pregnancy. In the first case, tissue from the placenta is taken for a sample. It will be checked for chromosomes. The risk of fetal loss with this procedure is about 0.9%. As for amniocentesis, during it a thin needle is inserted into the abdomen to obtain amniotic fluid. This procedure can harm the embryo only because of the mistake of the doctor. The risk varies within 0.5%.

It would not be superfluous to highlight the categories of women who need primary and secondary screening. These groups may have a high risk of having a child with a gene pathology. These categories of factors include:

Age above 30 years, if the pregnancy is the first;
- the presence of serious genetic anomalies;
- with two or more abortions;
- chronic infectious diseases;
- hereditary pathologies in parents;
- marriage with blood relatives;
- any radioactive exposure of one of the parents before or after conception.

Factors influencing the test

Biochemical screening can depend on a number of things. This applies to the analysis in both the first and second trimesters. Such factors must be taken into account in the final risk assessment. The most common cause of analysis error is maternal overweight. If she is obese, then her blood counts will definitely be elevated. If a woman has a significant underweight, then the results will be underestimated.

Multiple pregnancies are also a screening rejection factor. It is even theoretically impossible to calculate any risk here. The indicators will be elevated, but this is not always considered a genetic abnormality. The fact is that in this case, the test results are distributed over two or more embryos. Therefore, even repeated indicators will not lead to a clear picture of what is happening.

Bad habits can affect the analysis. This is especially true for smoking. Also, a failure can be recorded if a pregnant woman has a cold during the screening. It is worth noting that this type of analysis is prohibited in diabetes mellitus, as it always gives false results.

Screening preparation

The diagnosis of the body during pregnancy should always be approached seriously and thoroughly. However, preparation for testing is considered an equally important step, especially if this is the first blood screening. This analysis reveals specific markers that indicate the presence of chromosomal diseases. That is why it is important to do everything to eliminate even the slightest possibility of a false rejection.

Firstly, one day before testing, it is forbidden to eat foods such as smoked meats, citrus fruits, chocolate, fried, fatty and spicy foods. Otherwise, instead of blood serum, fatty elements are formed in the body. During the centrifugation procedure, it will be almost impossible to separate important cells. In any case, this will significantly complicate the test, it will be necessary to re-pass, which may adversely affect the fetus.

Analysis should always be done on an empty stomach. It is allowed to drink a little non-carbonated water 4-5 hours before the test.

Screening during the 1st trimester

The most suitable period for conducting an initial biochemical test is considered to be 10-13 weeks. Screening is not recommended at earlier dates. The price of such an analysis varies from 1800 to 2000 rubles. Based on the results of the primary test, specialists assess the health and development of the fetus, as well as the condition of the mother.

Screening during the 1st trimester can detect pathologies such as Down and Edwards syndromes, neural tube defects, heart disease, etc. Before evaluating the results, the doctor should always rely on personal examination data, such as blood pressure, temperature, mother's weight, etc. supporting factors. In parallel with screening, urine and blood tests are taken for infections. Confirmation of risks is done on the basis of ultrasound.

Screening during the 2nd trimester

Biochemical testing is carried out from 15 to 20 weeks of the term. At the end of the trimester, doctors do not recommend screening. The price of this procedure is about 3000 rubles. It includes several tests at once. First, chromosomal abnormalities are detected. Secondly, damage to the body of the embryo is detected, in particular in the abdominal cavity and spine. Also, the analysis allows you to predict the development of Down syndrome in the fetus.

Closer to the 20th week, the embryo is already quite large. Therefore, it is possible to take a sample of amniotic fluid with a minimum degree of risk. This type of screening is called amniocentesis. It is contraindicated to do with the tone of the uterus.

During the 2nd trimester, the most important types of research are ultrasound and biochemical screening.

Decoding and norms of indicators (1 trimester)

Perinatal diagnosis in the first weeks of pregnancy consists of determining several important blood and gene characteristics. The most significant of them are chorionic gonadotropin (abbreviated as hCG) and the PAPP protein. These are extremely important hormones on which the course of pregnancy directly depends.

From 10 to 12 weeks, the norm of hCG is considered to be from 20 to 95 thousand mU / ml. A deviation of 1-2 thousand units is allowed. The norm of hCG at week 13 is 15-60 thousand mU / ml.

Protein PPAP in the last month of the 1st trimester should be in the range from 0.3 to 6 mU / ml. At 10 and 11 weeks, the normal values ​​are from 0.32 to 3.73 units. By the end of the trimester, the protein level should rise to 0.71-6.01 mU / ml.

To exclude deviations due to the age and weight of the pregnant woman, the MoM coefficient is used. With the help of this medial indicator, the decoding of biochemical screening of the 1st trimester is facilitated. Here, the acceptable range is 0.5-2.5 units.

Decoding and norms of indicators (2nd trimester)

Biochemical screening of the 2nd trimester consists of blood characteristics such as hCG, alpha fetoprotein (AFP) and free estriol (E3). These are all important hormones that provide a detailed picture of fetal development.

Norms of biochemical screening of the 2nd trimester for AFP - from 15 to 95 U / ml. By the end of the period, it is possible to increase the indicators to 125. The level of hCG in the first half of the trimester should be from 8 to 58 thousand mU / ml. By the end of the period, the indicators fall significantly - from 1.6 to 49 thousand units.

Free estriol should be between 5.4 and 28 nmol/L. At the beginning of the period, the maximum threshold is 21 units. By the end of the trimester, the minimum allowable values ​​are 7.5 nmol / l.

If the final result of the analysis is presented as a ratio, then the risk is considered to be less than 1:380.

Reasons for hCG rejection

Biochemical screening results are not always 100% certain of the presence or absence of a genetic abnormality. Minor deviations from the norm can occur due to a number of reasons. However, you should not pay attention to them if all other tests are in order.

On the other hand, a significant increase in the level of hCG indicates a trophoblastic disease in the mother, as well as a multiple pregnancy. Decreased rates may be due to ectopic development of the fetus. If the fears are confirmed as a result of ultrasound, then the risk of a genetic disease becomes real.

Deviations of other indicators

A strongly elevated level of PPAP indicates a possible imminent miscarriage or infection. Reduced protein means the development of Down syndrome or Edwards.

Elevated AFP levels increase the risk of CNS defect, umbilical hernia, liver necrosis. If the level of this hormone is greatly reduced, there is a possibility of premature fetal death. Also, AFP can signal Down's syndrome.

Deviation of free estriol from the norm indicates the threat of premature birth, fetal anencephaly, placental insufficiency, liver disease in the mother.

Screening of the first trimester is a comprehensive diagnostic examination of pregnant women, which is performed from the 11th to the 13th week. Thanks to a double test at an early stage, it is possible to identify congenital pathologies in the development of the fetus, and also to find out what the likelihood of severe chromosomal disorders is. Not all women undergo screening in the 1st trimester, but we must remember that an unfavorable outcome of pregnancy is also possible.

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Who is required to undergo the first screening

There are separate groups of pregnant women who must undergo all studies without fail.
These include the following situations:

• If the woman's age is more than 35 years.
• If there is a threat of miscarriage.
• If previous pregnancies aborted on their own or stopped developing (missed pregnancy).
• If a woman works in a hazardous industry.
• If a child with congenital pathologies has already been born in the family.
• If in the first 12 weeks of pregnancy a woman suffered any infectious disease.
• If a woman abuses alcohol, drugs or cigarettes.
• If at least one of the parents suffers from a hereditary disease.
• If the parents are relatives.
• If a woman took medications that are prohibited during pregnancy.

All other women may voluntarily refuse to have the test.



How to prepare for the study

To get reliable results, a woman should perform the first screening at 10-14 weeks of pregnancy. The most accurate results are obtained in the period of 11-12 weeks. Therefore, it is important to correctly calculate the gestational age. It starts on the first day of the menstrual cycle. However, it will be better if it is calculated by a gynecologist. The first screening includes an ultrasound examination of the fetus and biochemical blood tests for beta-hCG and PAPP-A.


In order to obtain reliable data, you need to prepare for the study.

If the ultrasound examination is performed transabdominally (through the abdomen), then the bladder should be filled, it is advisable not to urinate 4 hours before the examination. If ultrasound is performed transvaginally, no special preparation is required.

If during the ultrasound the specialist detects a non-developing pregnancy, then the screening ends.

How to prepare for a biochemical blood test:

• Blood is taken from a vein on an empty stomach.
• Allergenic foods - chocolate, nuts, citrus fruits, seafood - should not be consumed 2-3 days before screening. For a while, it is worth giving up fatty, spicy and smoked foods.





What pathologies are detected on a double test

Thanks to this study, disorders in the development of the unborn child, as well as chromosomal abnormalities, can be detected at an early stage.


These include:

• Down syndrome is one of the most common genetic disorders.
• Lange's syndrome - numerous abnormalities in the development of the fetus. Even if the baby can survive, he will have severe mental retardation.
• Patau syndrome - severe pathologies of internal organs. Babies with this defect live only a few months.
• Edwards Syndrome. In normal fetal development, the umbilical cord includes two arteries and one vein. In the presence of this syndrome, ultrasound reveals one artery and one vein.
• Pathological development of the neural tube.
• Omphalocele (embryonic hernia). This is a protrusion in the navel, in which the internal organs are located.
• Anencephaly is a pathology in which the brain is absent.
• Anomalies in the structure of the heart.
• Cystic hygroma of the neck is a tumor-like formation that includes serous contents. It is well visualized on ultrasound in the fetal neck. In more than half of the cases, this disease is inherited.
• Megacystis is an enlarged bladder.

Deciphering the results obtained should only be a gynecologist.

Many experts believe that the first screening is more important than the second, because it is he who gives more accurate results (up to 95%, the second only 90%). If the results of the first test are good, then the second is most often not assigned.





Norms and interpretation of ultrasound

During the ultrasound examination, the specialist should carefully consider the structure of the embryo and compare the gestational age with different indicators.


To assess the development of the embryo, the following measurements must be taken.

KTR (coccygeal-parietal size) - an indicator that determines the distance from the head to the tailbone. It is used to determine the duration of pregnancy. The table shows the normal values ​​​​of CTE.

Deviations from the mean value do not always mean pathology. A few days ahead of the KTP indicates a large fetus. If the value is below the norm, the following situations are possible:

• late fertilization;
• frozen pregnancy (in the absence of a heartbeat);
• lack of certain hormones, such as progesterone;
• infection of the fetus;
• genetic abnormalities;
• cardiovascular diseases, pathologies of the thyroid gland and reproductive organs in the mother.

TVP of the embryo (collar space thickness). Normally, this indicator is from 1.5 to 2.7 mm. TVP is one of the most important markers of genetic abnormalities. The table shows the normal values ​​\u200b\u200bof this indicator. To evaluate this indicator, you need to know exactly the week and day of pregnancy. TVP cannot be determined in the second trimester. If the TVP is greater than 3 mm, then this is a sign of Down's or Edwards' syndrome. If the thickness of the collar space is more than 5 mm, then doctors insist on terminating the pregnancy, since the risk of chromosomal pathologies is quite high. But it is too early to talk about final forecasts. You must donate blood first. Only with poor results and the size of the cervical fold is more than 3 mm of blood, a chorionic biopsy is prescribed.



The size of the nose bone. This indicator can also determine the presence of Down syndrome. Determination of the size of the nasal bone is mandatory during the ultrasound. It can be measured starting from the 10-11th week of pregnancy, but it is recommended to estimate the size of the nasal bone only from the 12th week. Normally, this figure is not more than 3 mm. An enlarged bone or its complete absence indicates a high risk of having Down syndrome. If other indicators are normal, then the size of the nose is an individual feature of the child.

BDP (biparental head size) - the distance between the parietal tubercles, i.e. from temple to temple. This indicator increases in proportion to the period.

The increased size of this indicator indicates:

• Large fruit, if other indicators are increased.
• Growth of the child jumps. If other parameters are normal, then in a couple of weeks the BDP will be normal.
• The presence of swelling in the brain. This pathology is not compatible with life.
• Hydrocephalus due to an infectious disease of the mother. In this case, antibiotics will be prescribed and there is a chance to maintain a healthy pregnancy.

The reduced size indicates the underdevelopment of the brain or the absence of some areas.

The normal fetal heart rate is 150-180 beats per minute. It changes depending on the duration of pregnancy. A fast pulse may indicate Down's syndrome. Decreased heart rate should alert, it is additionally necessary to pass other tests.

The chorion is the membrane that surrounds the fetus. The thickness of the chorion at the very beginning of pregnancy is only a few millimeters, and at the 13th week it becomes the placenta. On screening ultrasound, the state of the chorion is analyzed. If the villi are underdeveloped, this indicates possible anomalies in fetal development. In addition to these parameters, it is necessary to assess the development of all organs, vessels of the umbilical cord and the placenta. For example, the bladder is visible on ultrasound only from the 11th week. If this organ is enlarged, then this indirectly indicates a violation in the development of the embryo.

Surely, many women want to know the sex of the child already at the first ultrasound. The size of the embryo is still very small, so you can determine the sex with a probability of 50% to 50%.

Norms and interpretation of the results of a biochemical blood test

This research is being carried outonly after an ultrasound. Biochemical parameters of blood depend on the duration of pregnancy and the norms change every day.




Blood is donated to determine such specific substances as beta-hCG and PAPP-A, and the MoM coefficient is also calculated.

Free beta-hCG in assessing the risk of developing chromosomal pathologies is more informative than just the hCG hormone. This hormone increases not only during pregnancy, but also with hormonal disorders or while taking certain medications. Thanks to beta-hCG, you can more reliably calculate the risk of having a baby with Down syndrome. The table shows the normal values ​​​​of this indicator. It should be remembered that in different laboratories they may vary slightly.

If the period was determined correctly, and beta-hCG is not normal, then the following deviations can be suspected, presented in the table:

PAPP-A is a substance produced by the placenta. During pregnancy, this figure is constantly growing. Deviations to a greater or lesser extent indicate the presence of various pathologies in the baby. If the PAPP-A value is lower than the average for the region, then this may indicate the development of Down syndrome or Edwards syndrome. If this figure is higher than normal, then there is a high risk of miscarriage or non-developing pregnancy. After the 14th week, PAPP-A will no longer be informative.

MoM is a coefficient that is calculated after determining beta-hCG and PAPP-A. The norm of this indicator from 9 to 13 weeks of pregnancy is considered a coefficient from 0.5 to 2.

If MoM is less than 0.5, then this indicates a high risk of Edwards syndrome, if more than 2, then Down syndrome. MoM is adjusted for the woman's history.



How Perinatal Risk is Calculated

In order for the screening results to be reliable, it is necessary to take a biochemical blood test and undergo an ultrasound scan on the same day, in the same medical institution, and always within the specified time frame for the study.



The risk of deviations is calculated in a special program, where the data of the conducted studies, the age of the woman and the individual characteristics of the body are entered. The result is given by the program as a fraction. For example, it turned out such a fraction 1:350. This means that out of 350 pregnant women with the same data, only one will have a child with pathologies. Depending on the value obtained, the conclusion may be:

• Positive. In this case, the risk of pathology is quite high and consultation of a geneticist is required. He will recommend additional studies for the final diagnosis or its refutation. To do this, a pregnant woman must undergo an amniocentesis, cordocentesis, or a biopsy of the chorionic villi. At an early stage of pregnancy, it is recommended to perform a biopsy of the chorionic villi, because the rest of the procedures are carried out for a longer period. In addition, the results will have to wait 3 weeks. If bad tests are confirmed, the doctor directs the woman to terminate the pregnancy, which will be carried out at 14-16 weeks. If you do an amniocentesis in the period of 16-17 weeks and wait for the result for another 3 weeks, then the abortion will take place only at the 20th week. At this stage, the baby is already beginning to move, and with proper care, if a premature birth takes place, it may even survive. At this time, they no longer have an abortion, but artificially induce childbirth, which negatively affects the woman's psyche. But it should be remembered that no doctor can force a pregnant woman to have an abortion, this should be a joint decision of the family.
• Negative. This means that the risk of pathology is low and additional studies are not needed. A woman should undergo a second screening at the specified time.

If the screening results show a high probability of pathology, do not panic. After all, this is not a final diagnosis, but just an assumption that can be refuted with the help of additional tests.




Reliability of screening and the need for it

There are quite conflicting opinions about the advisability of screening, even among doctors themselves. It should be remembered that screening does not carry accurate information - whether the child will be healthy or have any pathologies. Thanks to this study, you can only find out the likelihood of developing the disease.

This study makes it possible to undergo additional tests and terminate a pregnancy at a short time or, conversely, prepare for the birth of a child with special needs. In the absence of risks, the expectant mother can safely enjoy her pregnancy and not worry about the health of the baby.



Rarely, but there are situations when the screening results are false. When calculating risks, it is necessary to take into account many factors that affect the final result. False results can be caused by:

1. 1. Obese women. This condition provokes high levels of hormones, which affects the results of a double test.
2. 2. Pregnancy that occurred as a result of IVF. PAPP-A in this case is reduced by 10-15%.
3. 3. Pregnancy with two or more fetuses.
4. 4. The psychological mood of the woman during the study. Fear or anxiety distorts the results.
5. 5. Amniocentesis performed one week or less prior to screening.
6. 6. Diabetes mellitus, which lowers the level of hCG.

Factors affecting the calculation of the MoM coefficient should be identified at the preliminary examination and taken into account in the screening.