What is examined at the first screening. First trimester screening: results, risk calculation

Every pregnant woman faces screening in the 1st trimester, and then a second screening in the 2nd trimester. When I was pregnant for the first time, I was told that I needed to get screened. What it is and why was not explained in detail; I had to look for information on the Internet myself. After all, it is important to properly prepare for this study so that the results are as reliable as possible. But even careful preparation will not give you a 100% guarantee that the results will be correct.

Read in this article why screening in the 1st trimester, what studies this concept includes, how to prepare for them and how to decipher the results.

Screening in the 1st trimester of pregnancy is a special examination of the fetus for developmental defects. Screening is carried out from 10 to 13 weeks. In the antenatal clinic, absolutely all pregnant women are told about the need for such research and given directions. But a pregnant woman may refuse screening. In this case, she will be asked to write a written refusal.

I had both screening tests done during my first pregnancy and I still remember how worried and nervous I was. Because I knew a case where a woman was told that she would have a child with Down syndrome, but she did not have an abortion. As a result, a completely healthy child was born. Can you imagine what she went through during these 9 months?

Unfortunately, there are also errors of the opposite nature. Screening cannot always predict the birth of a sick child.

The screening itself consists of two studies - ultrasound and blood donation from a vein for biochemistry. Ideally, you should have these two treatments done on the same day to get more accurate results.

It is most important to screen the following categories of women in the 1st trimester:

those who have had 2 or more miscarriages or premature births;
those who had a previously frozen pregnancy;
who have relatives or children with genetic diseases;
age over 35 years;
if a woman had a viral or bacterial infection in the early stages;
if the woman took medications that should not be taken by pregnant women;
if the pregnant woman is in a close family relationship with the child’s father;
who has a “harmful” job;
for alcohol, tobacco and drug addiction.

What pathologies are detected at the first screening?

During screening in the 1st trimester, studies are carried out to identify the following pathologies:

Down syndrome. This is a chromosomal pathology when the 21st pair of chromosomes has three chromosomes instead of two. This syndrome is not rare; 1 case occurs in 700 fetuses. The risk of developing this syndrome increases with maternal age.
Patau syndrome. This is also a chromosomal pathology when there is an additional copy of chromosome 13 in the cells. The frequency of birth of children with this syndrome is 1 in 7000 or 10000. Children born with this pathology in most cases die before the age of 1 year because they have very severe developmental anomalies.
Edwards syndrome. This is a chromosomal disease when there are three chromosomes in the 18th pair of chromosomes. With this pathology there are many different developmental defects. This syndrome occurs in 1 child in 5000-7000.
Smith-Opitz syndrome. This is a hereditary disease that is caused by gene mutations. This disrupts the metabolism of cholesterol, which the embryo needs for the proper development of the brain, nervous system, limbs and other important functions. The incidence of the disease is 1 in 20,000-30,000.
Triploidy. This is a rare chromosomal abnormality. In this case, the fetus, instead of the required 46 chromosomes (23 from the father, 23 from the mother), has 69 chromosomes. In most cases, such pregnancies end in miscarriage; less often, children are born alive, but with multiple disorders.
De Lange syndrome. The cause of this disease is gene mutations. Damage to internal organs can vary in severity.
Omphalocele. This is a severe malformation when the child’s abdominal organs (intestines and liver) are located outside, in the umbilical cord, which is dilated.
Pathologies of the neural tube.
Timing of screening in the 1st trimester and preparation for it

The first screening must be done from the beginning of the 10th week to the end of the 13th week. And it is best to do it at 11-12 weeks. The gynecologist will tell you the best moment, based on the date of your last menstruation.

The first screening after the 13th week can no longer be considered reliable.

Preparing for an ultrasound. This procedure can be done in two ways: transvaginally and abdominally.

The transvaginal method is considered more accurate than ultrasound through the abdomen. This ultrasound is performed with a special sensor, which is inserted into the vagina. In this case, a condom is put on the sensor, which is lubricated with a special gel. This ultrasound determines whether there is a threat of miscarriage or whether there is a threat of placental abruption. No special preparation is required for such an ultrasound; it is done on an empty bladder.

If you prefer to do an ultrasound abdominally (through the abdominal wall), you will have to fill the bladder. To do this, half an hour before the test, drink 0.5-1 liters of still water and do not go to the toilet. For ultrasound in the second trimester, you no longer need to do this. It is advisable that the intestines be empty. That is, you do not need to eat at least 4 hours before the ultrasound.

Preparing for blood collection.

In order for the result to be as accurate as possible, you need to adhere to important rules. First, blood is donated on an empty stomach. This means that you should not eat for at least 6 hours before this test. You can drink some water, but don't get carried away.

Second, you need to go on a special diet one or two days before taking this test. On this day you cannot eat anything smoked, fatty, fried, or spicy. And also exclude chocolate, citrus fruits, and seafood.

By the way, it is better to exclude chocolate, citrus fruits, and strawberries from the diet of pregnant women altogether, so that the child is not prone to allergies. You can’t eat fatty foods, because it will be impossible to get normal serum from your blood, and the money for biochemistry will be wasted.

You need to come to donate blood with the results of an ultrasound scan, because the indicators in the blood test are closely related to the stage of pregnancy. You will receive the biochemistry results in a week and a half.

Decoding the results of the first screening

Ultrasound norms in the first trimester.

Coccygeal-parietal fetal size (CTF). The norm depends on the stage of pregnancy. See the table for the standards for this indicator.

Neck thickness (TCT). This indicator is considered very important when screening for genetic disorders.

A TVP size of more than 3 mm can be regarded as a risk of developing Down or Edwards syndrome.

Nasal bone.

This indicator is considered very important, because in Down syndrome this bone is not detected in the early stages.

Normally, at 10-11 weeks this bone is already detected on an ultrasound, but not measured. At 12-13 weeks, the nasal bone should be at least 3 mm. If this indicator is less than normal, and the collar zone is more, then this may indicate the development of Down syndrome.

Fetal heart rate (HR).

Biparietal size (BPR) - this is the distance between the parietal tubercles.

Also, ultrasound measures the size of internal organs, assesses the condition and placenta previa, and looks at the umbilical vessels. An ultrasound will determine the exact gestational age.

Decoding the results of a blood test for hormones

After the ultrasound, you will need to donate blood from a vein for hormones. Read here the norms for a biochemical blood test in the 1st trimester. This time the blood is examined for two markers - β-hCG (human chorionic gonadotropin) and PAPP-A (pregnancy-associated protein A).

Chorionic gonadotropin.

If the levels of this hormone reduced, then this indicates a pathology of the placenta or an increased risk of Edwards syndrome. Increased the amount of these hormones may be associated with the development of Down syndrome. And also this hormone will be more than normal during pregnancy with twins.

RARR-A. This is a protein that is produced by the placenta. The amount of these proteins increases with pregnancy.

Also, during a blood test, the MoM coefficient is calculated. Normally, this coefficient is 0.5-2.5 at this stage of pregnancy. If the pregnancy is twins, then MoM can be up to 3.5.

If MoM is below 0.5, this is interpreted as a risk of developing Edwards syndrome; MoM above 2.5 is a risk of developing Down syndrome.

How is the risk of congenital pathologies in the fetus calculated?

After passing the screening, you should be given the results of the examination. These results should indicate the risks for each individual syndrome. For example, Down syndrome - risk 1:380. This means that women with the same screening results give birth to 1 sick child per 380 healthy ones.

This calculation is made using a special computer program into which your ultrasound data, the results of a biochemical blood test, as well as age, individual characteristics of the body, concomitant diseases and pathologies, and harmful factors are entered. And taking all these parameters together, the program calculates the risks.

A risk of 1:250-1:380 is considered high. In this case, they are always referred to a geneticist for consultation. For an accurate diagnosis, parents will be asked to undergo additional tests: amniocentesis or chorionic villus biopsy. These studies can be life-threatening for the child (1% of children die after such an intervention). But after amniocentesis, they will tell you with almost a 100% guarantee whether the child is healthy or not.

If the risk of pathologies is low, then in the second trimester the pregnant woman will be sent for a second scheduled screening.

What affects screening results?

As I wrote above, screening results may be erroneous. There are factors that can affect the final result.

If a pregnant woman is obese, the amount of hormones will be increased, although this does not indicate fetal pathology. And if the expectant mother’s weight is too low, the amount of hormones will be less than normal.
With diabetes in the first trimester, the amount of hormones will be below normal. In this case, the results of the blood test will be unreliable.
If a woman is pregnant with twins, then she only undergoes an ultrasound, because the exact norms for hormones are unknown.
If pregnancy occurs as a result of IVF, the hCG level will be higher than normal, and PAPP will be lower.
The emotional state of the woman being examined can also be affected. Therefore, it is better not to think about the bad, but to tune in to good results and not worry.

Features of screening in the first trimester

Ultrasound screening for Down syndrome.

With this disease, in 70% of cases in the first trimester the nasal bone is not visible. But you should know that sometimes even in healthy children this bone may not be detected. The collar area is more than 3 mm. Disruption of blood flow in the venous flow. Increased heart rate, enlarged bladder. The upper jaw is smaller than normal. Facial features are smoothed.

Edwards syndrome.

Heart rate is below normal. The nasal bone is not identified. One umbilical cord artery instead of two. An omphalocele is present (when some internal organs are externally located in the hernial sac).

Patau syndrome.

Brain development is impaired. Heart rate increased. Omphalocele. The size of the fetus is smaller than expected at this stage.

It is better to undergo first trimester screening in one place to get the most reliable results. Proper preparation for screening and a positive attitude also play an important role. Remember that screening is not a diagnosis. And in case of increased risks, only additional research will help establish the truth.

Here are the basics you need to know about screening. May you have healthy children!

1st trimester screening is included in the general set of examinations during the gestation period to assess the child’s health and possible threats to pregnancy. Screenings are a common research method that applies not only to pregnant women: referrals for screening studies are also prescribed for newborns, as well as any population groups included in the risk group for developing any diseases, abnormalities, or dysfunctions.

Screening studies allow you to determine the likely possibility of pathology. In the first trimester of pregnancy, screening combines ultrasound examination and analysis of blood parameters, while interpretation of the results is carried out exclusively in a comprehensive analysis of both types of research.

First screening during pregnancy: period and timing of the study

During pregnancy, women are asked to undergo three screenings to identify and promptly correct possible deviations in the course of pregnancy or fetal development.

1 screening is carried out in the first trimester. The timing of pregnancy in the classic version is established on the basis of obstetric calculation, where the first day of the gestational period is considered the date of the beginning of the last menstruation before the onset of pregnancy. With the calendar method of determining the duration of pregnancy, experts start from the day of conception. However, since during physiological conception it is difficult to determine this date (the day of ovulation and the day of fusion of the egg and sperm may differ by 3-5 days), it is recommended to adhere to the obstetric technique, focused on the date of the last menstruation.

With a long menstrual cycle, the specialist can make changes to the screening dates, however, on average, the first screening test is carried out between 11 and 14 weeks of gestation, limiting the upper limit of the period to 13 weeks and 6 days from the date of the start of the last menstrual bleeding.

Why was this particular period chosen for the first screening? At 12 obstetric weeks, the border between the embryonic and fetal or fetal periods of development passes: the unborn baby passes from the embryonic stage to the fetus. The presence of formed structures and changes in the body make it possible to assign a new status to the future baby at the perinatal stage of development.

Also, this period is the minimum during which it is possible to identify the most common, although quite rare, deviations, as well as the reactions of the mother’s body to the development of a new life.

Screening – voluntary or obligatory?

Since early diagnosis of possible abnormalities allows you to quickly and effectively help the expectant mother correct possible negative consequences, screening studies during gestation are strongly recommended for all pregnant women, regardless of age, health status and the presence of healthy children. Deviations recorded during the study can occur spontaneously without correlation with the health of parents, relatives and lifestyle.

Despite the fact that the screening study is carried out on the direction of a gynecologist, you can refuse screening. This procedure is voluntary, although it is recommended by the Ministry of Health as part of the medical support of pregnancy for any woman.

If you refuse screening for one reason or another, you must remember that this study is useful for everyone, and especially for some categories of expectant mothers. High-risk groups include:

expectant mothers over the age of 35, regardless of previous experience of pregnancy and childbirth. This recommendation is associated with an increase in the number of possible chromosomal abnormalities during the onset of the aging process of the body;
women who have been diagnosed with a condition that threatens spontaneous miscarriage or miscarriage, frozen, non-developing pregnancy;
a history of infectious diseases (including influenza, ARVI during the first trimester);
parents with genetic disorders, women who, during previous pregnancies, had a high risk of genetic abnormalities, the presence of pathologies, or have children born with chromosomal abnormalities;
pregnant women forced to take medications that are restricted or prohibited for use during or immediately before gestation, certain types of vaccinations and medical procedures that briefly preceded pregnancy;
women whose pregnancy resulted from a close relationship;
women with bad habits: alcohol, drug addiction, etc.

A screening study does not pose a risk to the fetus or mother, so refusing diagnostics, which can reveal deviations that can be easily corrected at a given time, is at least unreasonable.

The study is carried out in public clinics free of charge. If you choose, you can undergo screening in any other clinic; if necessary, it is possible to repeat both the full study and one of its stages, if the timing of pregnancy allows.

What is included in the first perinatal screening?

Screening in the first trimester of pregnancy is limited to an ultrasound examination of the condition of the woman’s fetus and uterus, as well as a biochemical test of the pregnant woman’s blood, which determines the level of relevant hormones and the presence of certain markers.

The size of the fetus, the characteristics of the development of its body parts, bones, the presence of certain parts of the circulatory system in combination with the results of a blood test make it possible to confirm the correctness of the child’s development and the reaction of the mother’s body, or to suspect the possibility of some deviations.

How to prepare for the first screening?

Ultrasound examination of the fetus and uterus can be carried out using two methods: using a device with a transvaginal sensor or a transabdominal method of external examination through the surface of the peritoneum.

In the first case, preparation for the study consists of emptying the bladder immediately before the ultrasound; in the second, before the study it is necessary to fill the bladder, which will create the necessary darkening and contrast. The bladder should be filled approximately 30 minutes before the start of the study; the required volume of fluid is from 0.5 to 0.7 liters. It is preferable to drink non-carbonated drinking water and not visit the toilet, starting from 4 hours before the time of visiting a specialist until the end of the ultrasound.

During the procedure itself, the position of the fetus is an important factor. If the child lies in such a way that it is difficult to calculate the exact dimensions of some parts of the body, then the expectant mother may be asked to walk, bend over, tense and relax her stomach, imitate a cough, etc. At this time, it is sometimes possible to determine the sex of the unborn child, but for For a more accurate result, it is better to wait for the second ultrasound at a period above 20 weeks.

Blood biochemistry during screening of the first trimester should be carried out strictly after an ultrasound examination. The blood formula in the mother's body changes daily during pregnancy, and without correlation with the ultrasound date, a specialist will not be able to correctly interpret the analysis data.

For the most reliable results of a biochemical blood test, it is necessary to exclude all factors that may affect the functioning of various organs. Thus, preparation for the second stage of screening includes:

exclusion from the diet of foods that are potential allergens for all women (cocoa products, nuts, shellfish, citrus fruits, out-of-season vegetables and fruits) and identified allergens for pregnant women with a history of allergic reactions. It is necessary to notify a specialist about the presence of an allergy at the time of screening or shortly before it, this will allow a more accurate assessment of the test results. There is no need to talk about the need not to drink alcohol during pregnancy, but before screening this rule is especially important and applies even to small doses of alcohol on holidays;
The last meal should be 12 hours before blood sampling for testing, in the evening of the previous day. After getting up and before the analysis, you should not drink;
immediately before taking blood, you need to sit for 15-20 minutes, avoid stress and physical activity (jogging after the bus, climbing long stairs, etc.).

Failure to comply with the above rules may lead to distortions in test results, which may be incorrectly interpreted as a deviation in the development of the fetus or the course of pregnancy. Such unnecessary risks must be avoided.

Fetal parameters assessed by ultrasound during first trimester screening

During the ultrasound examination, the specialist evaluates the size of the fetus according to various indicators, as well as some important parameters of the child’s body at this period of development, features of the development and condition of the placenta and the mother’s uterus.

In the ultrasound results during the first screening, you can see the following designations:

KTR, or the length of the fetus from the crown to the tailbone: this is how the process of intrauterine development indicates the “growth” of the child, since the most characteristic position of the fetus - with legs bent and pulled to the chest, especially in the later stages - does not allow determining the length of the entire body. Full “height” can be roughly estimated based on the length of the femur bone, which, like the length of the shoulder and forearm bones, is an important indicator of fetal development;
OG is an indicator of the size of the fetal head, measured by circumference (calculated based on diameter);
BPR is an indicator of the bioparietal size of the head between the parietal bones. This indicator reflects both the development of the fetal head structures and, in later stages, allows us to make assumptions about the mother’s preferred method of delivery. With a large volume of the skull and a narrowed pelvis, a cesarean section will most likely be offered. The distance from the forehead to the back of the child’s head is also measured;
TVP is an indicator of the thickness of the nuchal space or cervical fold of the fetus, assessed only in the first trimester. By week 16, this formation is transformed into new organs, and during the first screening for this indicator, in combination with blood markers, the absence or increased likelihood of the presence of chromosomal disorders is diagnosed;
the thickness of the nasal bone as a probable indicator of the presence of genetic abnormalities is measured by ultrasound at 12-13 weeks; ultrasound at 11 obstetric weeks in most cases allows only to notice its presence and the beginning of its formation;
structural features of the brain, skull bones: this indicator describes how symmetrically and in accordance with the norm the skull and brain tissue of the fetus develop;
Heart rate, a measure of the heart rate or heartbeat, is assessed according to age-specific norms. Also, when examining the heart, if possible, the specialist examines the size and structural parts of the heart muscle. The location of the heart, stomach, large arteries and veins is also examined;
localization of the chorion (placenta), thickness of this organ. Later studies will also examine the presence and quantity of calcifications - inclusions indicating physiological aging of the placenta;
number of umbilical vessels;
volume and condition of amniotic fluid;
characteristics of the tone of the uterus and cervical pharynx.

Average values of basic parameters according to weeks of pregnancy:

Interpretation of the results of biochemical screening of the first trimester

The main indicators that specialists focus on when deciphering the results of a biochemical blood test at this stage are the level of human chorionic gonadotropin, the pregnancy marker hormone hCG, and plasma protein A, or PAPP-A.

The fetal membrane (chorion), which begins to form immediately after fertilization of the egg by the sperm, produces human chorionic gonadotropin on the very first day. However, this hormone reaches reference values for determining pregnancy no earlier than after 2 weeks. Highly sensitive rapid tests and blood tests for pregnancy determine the presence of this particular component.

In the first weeks of pregnancy, the level of human chorionic gonadotropin increases, doubling almost daily. The level of this hormone reaches its peak concentration at 11-12 weeks, then it decreases and stabilizes at insignificant levels.
High hCG in relation to the norm may indicate the following abnormalities and/or physiological conditions:

multiple pregnancy, in which the hormone is produced by several chorions;
maternal endocrinological diseases (diabetes mellitus) in history or developing during gestation;
manifestation of severe toxicosis in the first trimester;
chromosomal disorder - Down syndrome in the fetus.

A reduced level of human chorionic gonadotropin (hCG) relative to reference values may indicate the following disorders:

placental insufficiency;
presence of ectopic pregnancy;
increased risks of miscarriage and spontaneous abortion;
genetic disorder - Edwards syndrome in the fetus.

When assessing PAPP-A levels, only decreased values are significant. They may indicate a threat of miscarriage due to an inadequate response of the mother's immune system or insufficient functioning of the placenta, as well as some chromosomal abnormalities in the fetus.

Comprehensive interpretation of screening results

The first trimester screening results, after a full assessment of all indicators, will contain the following data:

risks of deviations associated with maternal age;
assessment and interpretation of maternal biochemical blood parameters;
the likelihood of the presence or occurrence of various diseases;
MoM value

Based on the results of an ultrasound examination and a biochemical blood test, specialists bring the data together and assign the so-called MoM index (multiple of median). This coefficient is formed on the basis of variable indicators characteristic of the range of results from studies of healthy women with a normal pregnancy and a timely developing fetus.

The norms for the first screening range from 0.5 to 2.5 units for a singleton pregnancy, and up to 3.5 if two or more babies are expected.
After calculating the IOM, the results are entered into a program that takes into account all factors that influence the health of the mother and child and the course of pregnancy: age, height-to-weight ratio, some diseases (in particular, diabetes), the presence of bad habits (tobacco smoking), number of pregnancy fetuses, physiological or extracorporeal method of conception, etc.

Based on the evaluation of all data, the program provides a probable risk of genetic abnormalities in the fetus. The result is presented as a proportion of 1:1000 for several genetic diseases, expressing the risk of occurrence of a given syndrome in each specific case. An index of 1:380 or more is considered a positive result of a low risk of violations; an index below 1:380 means an increase in risk.

But this indicator is not a final diagnosis, but an assessment of probabilities. So, if a specialist’s conclusion contains an index of 1:70 for Down syndrome, this means that only 1 out of 70 women with similar results gives birth to a child with developmental disorders. In 69 cases, pregnancy proceeds without abnormalities and ends in the birth of a healthy child.

The following factors influence the distortion of results:

non-compliance with the rules of preparation for biochemical analysis;
outdated ultrasound equipment;
in vitro fertilization;
endocrinological disorders (diabetes mellitus of both types);
multiple pregnancy;
increased maternal body mass index (overweight).

What to do if the screening results are disappointing?

Many women are afraid to undergo the “first exam” in the life of the fetus, fearing both hearing negative news and hasty prescriptions and even pressure to terminate the pregnancy. If you have any doubts about the results, you can undergo additional screening, following the rules of preparation and alternation of ultrasound and biochemistry, and evaluate the condition and results as a whole.

In fact, “high risk” is diagnosed at rates between 1:250 and 1:380 for any syndrome, which means a slightly increased, but not necessarily, likelihood of a child having genetic abnormalities. With such indicators, it is recommended to lead a healthy lifestyle, regularly see a gynecologist and undergo genetic counseling.

In some cases, a genetic specialist may suggest undergoing additional examination for an accurate diagnosis (chorionic villus biopsy, amniocentesis, cordocentesis), on the basis of which recommendations for parents will be made.

Screening is a study carried out comprehensively on a specific group of people, in this case, pregnant women at different stages. Screening in the first trimester includes ultrasound diagnostics and biochemical blood tests. The study is aimed at identifying possible genetic abnormalities, as well as pathologies of fetal development.

How is the study carried out and for how long?

In the first trimester, screening, including routine ultrasound, is carried out at 11–13 weeks of pregnancy, which is considered the optimal period for the study. If an ultrasound is performed earlier than this period or, conversely, later, the interpretation of the results may be unreliable.

Of course, a woman can write a refusal to conduct research, even despite the order of the Ministry of Health of the Russian Federation in force since 2000, but such a decision will be extremely risky and even negligent in relation not only to her health, but also to the health of the unborn child.

First trimester screening includes two types of research:

Ultrasound diagnostics.
Biochemical blood test.

Ultrasound examination in the first trimester of pregnancy requires some preparation. To conduct the study in the usual (superficial) way, when the sensor of the device slides over the belly of the expectant mother, her bladder must be full, for which it is necessary to drink about half a liter of clean still water 1-1.5 hours before the start of the procedure, or 3– Do not urinate 4 hours before the ultrasound.

If the doctor performs the procedure transvaginally, when a special sensor of the device is inserted into the vagina, then no special preparation is required. The pregnant woman must go to the toilet before starting the procedure.

A biochemical blood test is the second stage of screening and is carried out only after an ultrasound. This condition is important, since the obtained indicators always depend on the stage of pregnancy and change every day, and the exact period can only be determined using ultrasound. This condition must be met in order to obtain a correct interpretation of the study indicators and establish compliance with the necessary standards.

At the time of taking blood for analysis, the woman must have ready-made results of the first part of the study, which will indicate the exact duration of pregnancy. If the ultrasound test procedure showed regression of the pregnancy or its fading, then there is no point in carrying out the second part of the screening.

A biochemical study requires preparation so that the doctor can obtain accurate indicators and determine their compliance with standards. Blood sampling from a vein is carried out strictly on an empty stomach.

Approximately 2-3 days before visiting the treatment room, it is necessary to: exclude from the diet sweets, smoked foods, fried and fatty foods, as well as foods that are potential allergens, for example, nuts, chocolate, citrus fruits, seafood.

Failure to comply with these conditions often leads to unreliable research results.

What can you learn from screening?

In order for the ultrasound interpretation to be reliable and informative, it is necessary to carry out the procedure no earlier than the 11th week of pregnancy, but no later than the 13th.

The position of the fetus should be comfortable for inspection and measurement. If the baby's position does not allow the ultrasound procedure, the woman is asked to turn on her side, walk around, do a few squats, or cough to get the baby to turn over.

Indicators that should be examined during an ultrasound scan in the first third of pregnancy:

Coccygeal-parietal size (CTP). The measurement is taken from the parietal point of the head to the tailbone.
Biparietal size (BPD) is the distance between the tubercles of the parietal zone.
Head circumference.
Distance from the back of the head to the frontal area.
The structure of the brain, the symmetry of the arrangement of the hemispheres, the closure of the cranium.
Thickness of the collar zone (TVP).
Heart rate (HR).
The size of the heart, as well as the largest vessels.
The length of the bones of the shoulders, thighs, lower legs and forearm.
The thickness of the placenta, its structure and location in the uterus.
The location of the umbilical cord and the number of vessels in it.
Volume of amniotic fluid.
Uterine tone.
Condition of the cervix and its internal os.

When an ultrasound is performed ahead of schedule, the doctor cannot assess the size of the nasal bone; the CTE of the fetus ranges from 33 to 41 mm, which is not enough to conduct an adequate study. Heart rate during this period ranges from 161 to 179 beats, TVP from 1.5 to 2.2 mm, and BPR is 14 mm.

Standards for deciphering indicators at this time:

At week 11, the fetal nasal bone is visible, but its size cannot always be assessed. The baby's CTE is from 42 to 50 mm, BPR is 17 mm, TVP is from 1.6 to 2.4 mm, and heart rate is from 153 to 177 beats.
At week 12, the size of the nasal bone is 3 mm or just over. CTE is in the range of 51-59 mm, BPR is 20 mm, TVP is from 1.6 to 2.5 mm, and heart rate is from 150 to 174.
At 13 weeks, the nasal bone size is more than 3 mm. CTE ranges from 62 to 73 mm, BPR is 26 mm, TVP is from 1.7 to 2.7, and heart rate is from 147 to 171 beats per minute.

Biochemical screening determines a number of important indicators, one of which is human chorionic gonadotropin β-hCG, produced by the fetal membrane. It is this hormone that allows you to determine the presence of pregnancy at the earliest stages using a special test strip.

From the beginning of pregnancy during its normal course, the level of β-hCG gradually increases, reaching its maximum value by the 12th week, after which it decreases. During the second half of the term, β-hCG levels remain at the same level.

The normal β-hCG levels are:

Week 10: from 25.80 to 181.60 ng/ml;
week 11 from 17.4 to 130.3 ng/ml;
week 12 from 13.4 to 128.5 ng/ml;
Week 13 from 14.2 to 114.8 ng/ml.

Elevated values are observed with Down syndrome in a developing fetus or when the expectant mother has a severe form of toxicosis, as well as diabetes mellitus.

Decreased readings may indicate placental insufficiency (which is usually determined by ultrasound) or that the fetus has Edwards syndrome.

The second important indicator is protein-A (PAPP-A), which is associated with pregnancy, since this protein is produced by the placenta and is responsible for its proper functioning and development.

The following data are considered normal indicators of PAPP-A:

From 10 to 11 weeks from 0.45 to 3.73 mIU/ml;
From 11 to 12 weeks from 0.78 to 4.77 mIU/ml;
From 12 to 13 weeks from 1.03 to 6.02 mIU/ml;
From 13 to 14 weeks from 1.47 to 8.55 mIU/ml.

If the readings are below normal, this may indicate not only a threat of miscarriage, but also the presence of Edwards, Down syndrome or Cornelia de Lange syndrome in the fetus. In some cases, an increase in protein levels is observed, but this does not have significant diagnostic and clinical significance.

Calculation of MoM coefficient

This indicator is calculated based on the results of the research. Its value indicates the degree of deviation of test results from the established average norms, which range from 0.5 to 2.5 for singleton pregnancies and up to 3.5 for multiple pregnancies.

In different laboratories, when examining the same blood sample, the indicators may differ, so you cannot evaluate the results yourself; only a doctor can do this.

When calculating the coefficient, it is necessary to take into account not only the tests, but also the age of the expectant mother, the presence of chronic diseases, diabetes, bad habits, the weight of the pregnant woman, the number of fetuses developing inside, as well as how the pregnancy occurred (naturally or with the help of IVF). The risk of developing pathologies in the fetus is considered high when the ratio is below 1:380.

It is important to correctly understand the meaning of this ratio. For example, if the conclusion states “1:290, high risk,” this means that among 290 women with the same data, only one had a child with a genetic pathology.

There are situations when averages deviate from the norm for other reasons, for example:

if a woman is overweight or severely obese, hormone levels are often elevated;
with IVF, PAPP-A indicators will be lower than the general average, and β-hCG, on the contrary, will be higher;
an increase in normal hormone levels can also be observed when the expectant mother has diabetes;
for multiple pregnancies, average norms have not been established, but the level of β-hCG is always higher than during the development of one fetus.

Carrying out research in the first trimester allows us to determine the presence (absence) of many pathologies in the developing fetus, for example:

Meningocele and its varieties (pathologies of neural tube development).
Down syndrome. Trisomy 21 occurs in one case out of 700 examinations, but thanks to timely diagnosis, the birth of affected infants has decreased to 1 in 1100 cases.
Omphalocele. With this pathology, a hernial sac forms on the anterior abdominal wall of the fetus, into which part of the internal organs enters.
Edwards syndrome, which is trisomy 18. Occurs in one in 7,000 cases. It is more common in babies whose mothers are over 35 years old at the time of pregnancy. When performing an ultrasound, the fetus is observed to have an omphalocele, a decrease in heart rate, and the nasal bones are not visible. In addition, disturbances in the structure of the umbilical cord are also detected, in which instead of two arteries there is only one.
Patau syndrome, which is trisomy on chromosome 13. It is very rare, about one case per 10,000 newborns, and, as a rule, about 95% of infants with this syndrome die during the first months of life. When performing an ultrasound in these cases, the doctor notes a slowdown in the development of long bones and the brain, an omphalocele and an increase in the fetal heart rate.
Triploidy, which is a genetic abnormality characterized by a triple set of chromosomes, which is accompanied by the occurrence of many developmental disorders.
Smith-Opitz syndrome. The disorder is an autosomal recessive genetic disorder that causes metabolic disturbances. As a result, the developing fetus develops many defects and pathologies, autism, and mental retardation. The syndrome occurs in one case out of 30,000.
Cornelia de Lange syndrome, which is a genetic abnormality that causes mental retardation in the unborn child. Occurs in one case out of 10,000.
Fetal anencephaly. This developmental pathology is rare. Babies with this disorder can develop inside the uterus, but they are unable to live and die immediately after birth or later in the womb. With this anomaly, the fetus lacks the brain and bones of the cranial vault.

Screening in the first trimester allows us to identify many chromosomal diseases and developmental disorders in the unborn child in the early stages of pregnancy. Screening allows you to reduce the percentage of babies born with congenital anomalies, as well as save many pregnancies in which there is a threat of termination by taking timely measures.

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The position obliges. Don’t drink or smoke, don’t mindlessly take medications, watch what you eat. Do not wear clothes close together, avoid risky situations and dangerous places. Also, visit your doctor regularly and get tested. Some of the rules that a pregnant woman has to obey may be unusual or even unpleasant, but most will agree that they are beneficial for mother and child.

Additional tests - are they necessary?

Standard laboratory tests that are performed almost constantly throughout pregnancy are general blood and urine tests. In the first trimester, blood is also taken for biochemistry, sugar, blood type, Rh factor, AIDS, syphilis, and hepatitis. An electrocardiogram is also done and a vaginal smear is taken to check for infections. In addition to the mandatory tests, the doctor may suggest other studies in the early stages of pregnancy. Most often this is an ultrasound, checking for TORCH infections, biochemical screening of the 1st trimester. They are carried out at the request of the patient or at the insistence of the doctor. There are also more specific studies for this period, but they are prescribed only if there are certain indications.

While the effect of ultrasound on the fetus can still be debated, donating an extra portion of blood is completely harmless. But the data obtained as a result of special blood tests are considered very valuable, since there is a chance to detect possible pathologies in the early stages and immediately begin to optimize the situation. Unfortunately, in most of our clinics it is not possible to conduct laboratory tests such as biochemical screening of the 1st trimester and identification of the TORCH complex. Therefore, these tests often have to be taken in private laboratories at your own expense. This is one of the main reasons why such a diagnosis is not necessary.

What is biochemical screening 1st trimester

Biochemical screening of the 1st trimester is the measurement of certain substances in the blood, which helps to identify disorders in the formation of the central nervous system of the fetus, as well as Down and Edwards syndromes. The study focuses on levels of plasma pregnancy-associated protein A (PAPP-A) and human chorionic gonadotropin (hCG), which is familiar to women from pregnancy tests. Sometimes biochemical screening of the 1st trimester is also called a “double test”, since it determines the amount of two placental proteins. In the second trimester, the analysis is carried out on the basis of three indicators, calling it, accordingly, a “triple test”.

This is usually done just in case, since no one is fully insured against such troubles. However, there are also risk groups for which undergoing biochemical screening in the 1st trimester is especially important:

Mature women who have reached the age of 35;
Consanguineous couples;
Families with a child or relative with chromosomal abnormalities or genetic pathologies;
Couples in which one or both spouses received a dose of radiation before conception work in hazardous enterprises;
Patients with a threat of miscarriage or who have previously had miscarriages, as well as after viral or bacterial infections (including the reproductive system);
Women who took certain medications that are harmful to the fetus in early pregnancy.

Also, this analysis may be insisted on due to deviations from the norm according to ultrasound data. But even if you do not have any indications, it will not be superfluous to take this test, if, of course, opportunities allow. There is no harm from this, but both you and your doctor will be calmer.

Biochemical screening 1st trimester - transcript

It is important to remember that changes in the levels of some special substances in the blood may indicate the presence of fetal pathologies, but are not an absolutely reliable source for diagnosis. The final decision is made based on comprehensive information. So it is better to entrust the interpretation of the data to a specialist. But when picking up test results from the laboratory, few people manage not to look at them - especially when it comes to such important issues.

During biochemical screening of the 1st trimester, the norm for each substance is determined based on the duration of pregnancy. Typically, blood is given for this test between 9-13 weeks.

HCG norm by week:

9-10 weeks –20,000-95,000 mU/ml; 23.6-193.1 ng/ml;
11-12 weeks – 20,000-90,000 mU/ml; 13.4-130.4 ng/ml;
13-14 weeks – 15,000-60,000 mU/ml; 8.9-114.7 ng/ml.

Norm PAPP-A by week:

9-10 weeks –0.32-2.42 mU/ml;
11-12 weeks – 0.46-4.76 mU/ml;
13-14 weeks – 1.03-8.54 mU/ml.

In addition to quantitative data, another coefficient is displayed, which conditionally shows the norm of ratios for biochemical screening of the 1st trimester - MoM (English abbr., multiple of the average value). Ideally, this coefficient should be close to one, but values in the range of 0.5-2 are a good result. If you really want to understand the situation in advance, then it is better to be guided by this simple indicator and leave complex calculations to your doctor.

Biochemical screening data in the 1st trimester can be influenced by a number of factors:

Multiple pregnancy;
The patient’s weight is both low and overweight;
Pregnancy as a result of in vitro fertilization (IVF, so-called artificial insemination);
Taking medications;
Feeling unwell during the test - for example, a cold;
Diabetes mellitus in pregnancy;
Smoking by the expectant mother;
Difficulties in pregnancy, threat of failure.

But even if there is something wrong with the analysis results that, in your opinion, should be normal, do not rush to conclusions. Decoding the biochemical screening of the 1st trimester is, firstly, the task of professionals, and not women who are impressionable due to their position. And secondly, this is only one of the methods for early diagnosis of deviations, which does not provide a ready-made and categorical diagnosis. So, do not panic under any circumstances, but simply go to see a doctor for clarification.

– mass examination of women, which is done at 11–13 weeks of pregnancy. The first screening allows us to identify congenital abnormalities of the fetus, as well as the risk of its birth with severe genetic disorders.

Screening in the first trimester includes an ultrasound examination and a biochemical blood test for specific indicators (β-hCG and PAPP-A). All pregnant women without exception are subject to screening. In this case, the woman has the right to refuse such an examination.

But, it should be remembered that refusal of screening may lead to adverse pregnancy outcomes.

In what cases is screening necessary?

There are risk groups of pregnant women who must undergo prenatal diagnosis.

The first screening is carried out in the following cases:
All women over 35 years of age.
If there have been miscarriages or undeveloped (frozen) pregnancies in the past.
In the presence of harmful occupational factors.
Risk of miscarriage.
If the family already has a child with congenital pathologies or chromosomal disorders. Or such abnormalities were diagnosed in previous pregnancies.
Women who have had infectious diseases in the first trimester.
Women who suffer from alcoholism, smoking or drug addiction.
If there are hereditary diseases in the family of one of the parents.
The presence of a family connection between the parents of the unborn child.

Women who have taken pharmaceuticals that are contraindicated for use during pregnancy.

Procedure for the first screening

To undergo a reliable first screening, the 1st trimester has a certain framework for this. The first prenatal diagnosis is carried out from the 10th week of pregnancy until the 14th week. The most reliable indicators will be those obtained at weeks 11–12. It is very important that the deadline is set correctly. A gynecologist will do this and determine when it is best to undergo the first screening.

In order to undergo a perinatal examination, it is necessary to properly prepare for the examinations. If ultrasound is performed with a vaginal sensor, then no special preparation is required. If an ultrasound is performed through the abdomen, the following rules must be followed:
The bladder should be full.

Do not urinate 4 hours before the ultrasound.

If an undeveloped pregnancy is detected on ultrasound, the examination is stopped.

Before donating blood, it is necessary to do an ultrasound of the fetus. This is the most important condition, since the indicators in the biochemical blood test directly depend on the duration of pregnancy.
It is necessary to take a blood test from a vein strictly on an empty stomach. If necessary, you can take food with you and eat after the blood test.
A couple of days before the biochemical examination, it is necessary to exclude all potential allergens from the diet. They can be seafood, nuts of any kind, chocolate. You should also avoid eating spicy, fatty and smoked foods.

If the basic rules are not followed, the results of the first screening may be incorrect.

What pathologies can be detected during the first screening?

Screening in the 1st trimester reveals gross developmental disorders of the child and chromosomal pathologies. During screening, the following abnormalities can be detected or suspected:

Down syndrome is the most common genetic abnormality.
Lange's syndrome. It is characterized by multiple developmental defects. If the baby survives, then he has severe mental retardation.
Patau syndrome. Characterized by severe damage to the child’s organs. Such children die in the first months after birth.
Edwards syndrome. Ultrasound reveals an anomaly in the development of the umbilical vessels - 1 artery and 1 vein. Normally, the umbilical cord contains 3 vessels - 2 arteries and 1 vein.
Malformations of the neural tube in the fetus.
Omphalocele is a hernial protrusion in the area of the umbilical ring, which includes internal organs.
Anencephaly is the absence of a brain.

All interpretations based on the results obtained are made by a gynecologist.

Interpretation of ultrasound results at the first screening

At the first screening during ultrasound, the following indicators are assessed:

The distance from the crown to the coccyx (KTR), which normally ranges from 33 to 73 mm, depending on the stage of pregnancy. Below is a table showing the CTE standards:

Fetal TVP (nuchal translucency thickness).

Normally, TVP is from 1.5 to 2.7 mm. During screening, TVP is a very important marker of genetic disorders. The table below shows the TVP standards:

If the TVP result is more than 3 mm, then this can be regarded as a sign of Edwards or Down syndrome.

Nose bone size.

This is a marker by which Down syndrome can be suspected. Determination of the nasal bone is necessarily included in the screening of the first trimester. According to ultrasound, the nasal bone is normally determined from 10 to 11 weeks. Bone size is assessed from 12 weeks. Normally, the nasal bone should be more than 3 mm. The absence of the nasal bone and an increase in TVP are a clear sign of Down syndrome.

Biparietal size (BPR).

Ultrasound determines this size as the distance between the parietal tubercles. By the end of the first trimester, the BPR result is normally more than 20 mm.

Fetal heart rate.

Heart rate also differs depending on when screening is done in the first trimester. Normal heart rate ranges from 150 to 180 beats per minute.

The development of the internal organs of the fetus, umbilical vessels, and placenta is assessed.

Decoding the results of a biochemical blood test

After a successful ultrasound, it is necessary to take a blood test for the content of specific substances: β-hCG and PAPP-A. In addition, the MoM coefficient is calculated.

Free β-hCG is a fetal specific hormone. Screening in the 1st trimester allows you to determine its maximum values. Determining the level of β-hCG allows you to most reliably calculate the risk of Down disease. Below is a table showing normal values for β-hCG levels:

It is important to remember that normal β-hCG levels may vary from laboratory to laboratory.

PAPP-A is a protein substance produced by the placenta. During gestation, the level of a specific protein constantly increases. Deviations from the normal values presented in the table may indicate the presence of abnormalities in the child.

Do not forget that PAPP-A values in each laboratory also differ.

The MoM coefficient is calculated when determining β-hCG and PAPP-A. Can be used instead of standard units of measurement. Its indicators normally range from 0.5 to 2 from 9 to 13 weeks. If the MoM is below 0.5, then this may indicate a risk for Edwards syndrome in the child. When MoM exceeds 2, this indicates possible Down syndrome.

Calculation of perinatal risk

In order for first trimester screening to be as reliable as possible, tests and ultrasounds must be taken in one institution. The risk of deviations is calculated based on the results of β-hCG, PAPP-A, the age of the pregnant woman, individual characteristics of the body, harmful factors, and concomitant pathologies. The obtained data is entered into a computer, into a special program that calculates risks. The program produces the final result in the form of a fraction. For example, the program gave a risk of 1:400. The decoding will be as follows: out of 400 pregnancies with the entered indicators, 1 baby will be born with a pathology. Depending on the value obtained, conclusions may be as follows:

Positive test. It means that during this pregnancy there is a high risk of having a child with a pathology. In this case, a genetic consultation is carried out. The issue of additional examination to establish or refute the diagnosis is being decided. In this case, amniocentesis or chorionic villus biopsy is performed.
Negative test. This means that the risk of pathologies is low and there is no need to conduct additional examination. In this case, the pregnant woman undergoes routine screening in the 2nd trimester.

First trimester and screening for Down syndrome

Down syndrome in a fetus can be suspected as early as 10–11 weeks. When performing an ultrasound, the following characteristic signs of this syndrome are revealed:

Thickening of the TVP is more than 3 mm. An abnormal TVP may also indicate other genetic disorders.
Absence of the nasal bone in 70% of cases. It is important to know that even in healthy children in the early stages, the nasal bone may not be identified.
Impairment of blood flow through the ductus botalli.
Hypoplasia (reduction) in the size of the upper jaw.
Bladder enlargement.
Increased fetal heart rate.
Pathology of umbilical cord vessels: one artery and one vein.

First trimester screening is an important stage of examination during pregnancy. With its help, you can exclude or identify severe pathologies in a child, often incompatible with his life. In order for the indicators to be reliable, it is necessary to follow the doctor’s recommendations and undergo screening within the prescribed period.

If screening results reveal a high risk of pathologies, do not panic. It is necessary to contact a specialist who will prescribe additional examination. It is important to remember that high risk is not a diagnosis, but only an assumption, which is often refuted after additional examinations.