At what stage of pregnancy is the second prenatal screening performed, what does ultrasound show? Second screening during pregnancy: timing, what they look for and norms When the 2nd screening is done.

The capabilities of modern medicine allow the expectant mother to learn as much as possible about the course of pregnancy, eliminate possible deviations in its course, and determine that something in the development of the baby will go wrong. Today, pregnant women have the opportunity, if desired, and sometimes even necessary, to undergo a wide variety of examinations and pass all sorts of tests, which make it possible, with varying degrees of probability, to establish that there is no threat to the normal and natural formation of the fetus. One of the comprehensive methods of examining a pregnant woman is the so-called prenatal screening.

Second screening during pregnancy: timing

Screening research in the CIS has been carried out relatively recently, but due to its rich information content, it is actively used in the practice of managing pregnant women. makes it possible to identify risk groups for complications during pregnancy, and also allows us to identify risk groups for the development of congenital pathologies in the fetus. The first screening test is carried out in the first trimester, and the second screening during pregnancy, respectively, in the second trimester.

Experts consider the most “successful” time for the first screening to be 12-13 weeks, although this study can be carried out in the period from 11 to 14 weeks of pregnancy. The time frame for the second screening during pregnancy is from 16 to 20 weeks, although doctors call 16-17 weeks of pregnancy the most optimal and most informative for it.

Second screening during pregnancy: indicators

The purpose of the second screening is to identify a risk group among pregnant women when the likelihood of developing chromosomal abnormalities in the fetus is quite high.

Screening can be ultrasound (detects possible fetal abnormalities using ultrasound); biochemical (study of blood markers); and combined - consists of ultrasound and biochemical examination. As a rule, an ultrasound examination is carried out as part of a screening study at the end of the second trimester of pregnancy, and the second screening during pregnancy itself consists of a blood test for various indicators. The results of an ultrasound scan performed on the eve of screening in the second trimester of pregnancy are also taken into account.

The algorithm of actions during screening looks like this: after donating blood and ultrasound, a pregnant woman fills out a questionnaire, where she indicates personal data, which will be used to calculate the gestational age and the risks of developing defects. Analyzes are performed taking into account the duration of pregnancy, after which the information received is processed by a computer program to calculate risks. And yet, even the results obtained cannot be considered a final diagnosis, after which we can absolutely say about the presence of risks, if they have been established. For more detailed and accurate information, the doctor should refer the pregnant woman for additional tests and a consultation with a geneticist.

If we talk specifically about the second screening during pregnancy, it is a biochemical study of the mother’s blood using special tests. The so-called “triple test” is an analysis of the blood level of substances such as human chorionic gonadotropin (hCG), alpha-fetoprotein (AFP), and free estriol. If the second screening during pregnancy also includes a blood test for inhibin A, then the test is already called “quadruple”. A study of the concentration of these specific hormones and proteins in the blood of a pregnant woman makes it possible, with a certain degree of probability, to talk about the risk of developing in the fetus such as (trisomy 21), Edwards syndrome (trisomy 18), neural tube defects (spinal canal cleft and anencephaly).

Second trimester screening results may indirectly be a sign of certain abnormal conditions for fetal development and pregnancy complications. For example, an elevated level of hCG may indicate chromosomal pathologies, the risk of developing preeclampsia, or the presence of diabetes mellitus, O multiple pregnancy. Reduced hCG, in turn, may be a sign of abnormal development of the placenta. An increase or decrease in AFP, and with it inhibin A in the mother’s blood serum, indicates disturbances in the normal development of the fetus and possible congenital pathologies - open neural tube defects, the likelihood of trisomy 21 or trisomy 18. A sharp increase in alpha-fetoprotein can also lead to fetal death . Changes in the level of free estriol, a female steroid hormone, may be a signal of dysfunction of the fetoplacental system; its insufficient amount indicates possible disturbances in fetal development.

Even if the results of the second screening during pregnancy are characterized as unfavorable, you should not despair and immediately sound the alarm. They only indicate a possible risk of anomalies, but are in no way a final diagnosis. If at least one screening indicator does not correspond to the norm, it is important to undergo an additional comprehensive study. In addition, several factors that alter the results of the examination may influence the performance of a screening examination. These are: in vitro fertilization, pregnancy weight, diabetes mellitus and any other maternal diseases, bad habits, for example, smoking during pregnancy. It is not at all advisable to conduct a biochemical blood test as part of screening: the indicators in this case are overestimated, and the accuracy of the risk is extremely difficult to calculate.

Especially for- Tatyana Argamakova

Modern methods of monitoring the health of the expectant mother during pregnancy involve three screenings -. Each comprehensive examination includes completion and evaluation of the results.

Dates

The optimal time for the second screening is from before pregnancy. At this time, the doctor has the opportunity to determine the presence of defects or disorders that could not be identified during the first examination.

Many experts recommend undergoing a second screening examination in order to be able to undergo additional examination or make an appointment with a geneticist if a high degree of likelihood of developing any diseases in the fetus is detected.

Research types

The second prenatal screening consists of the following types of examinations:

• – performed using a transabdominal sensor (through the skin of the abdomen). During the procedure, the doctor evaluates not only the growth and development of the fetus, but also the condition.
• . In laboratory conditions, a specialist determines the content, and.

First, it is advisable for the expectant mother to undergo an ultrasound scan, and based on the results of this examination, the doctor decides on the need for a blood test from a vein.

Preparing for screening

In preparation for the second prenatal screening, much fewer requirements are placed on the woman than before the first examination. There is no need to specifically fill the bladder with liquid, because the fetus is already surrounded in sufficient quantities at this time.

The condition of a pregnant woman’s intestines is also not of great importance during an ultrasound scan, since this organ is moved back enlarged. However, the day before the examination, it is advisable to avoid foods such as:

• citrus;
• fried and fatty foods.

important The morning before donating blood from a vein, you must refrain from breakfast.

Standard values

During the second screening, the doctor pays great attention to determining a number of indicators and hormone levels in the blood of a pregnant woman, and then compares them with the recommended standard values. Depending on the stage of pregnancy, these data should be:

• – determined to assess the size of the fetal head. The standard values ​​for this indicator are as follows: – 35 mm; – 39 mm; – 42 mm; – 44 mm; – 47 mm.
• Thigh Length(DB) should approach the following norm: at week 16 – 22 mm, at week 17 – 24 mm, at week 18 – 28 mm, at week 19 – 31 mm, at week 20 – 34 mm.
• Abdominal girth (AB) should be: at week 16 – from 88 to 116 mm; at week 20 – from 124 to 164 mm.
• determined starting from week 20 - during this period it should be from 16.7 to 28.6 mm and have a “zero” degree of maturity.
• can range from 80-200 mm (at 16 weeks) to 93-130 mm (at 20 weeks).
• should be: at week 16 – from 10 thousand to 58 thousand honey/ml; at 17-18 weeks – from 8 thousand to 57 thousand honey/ml; at week 19 – from 7 thousand to 49 thousand honey/ml; at week 20 – from 4.7 thousand to 47 thousand honey/ml.
• must meet the following indicators: at week 16 – from 5.4 to 21 nmol/l; at 17-18 weeks – from 6.6 to 25 nmol/l; at 19-20 weeks – from 7.5 to 28 nmol/l.
• is: for a period of 16-19 weeks – from 15 to 95 U/ml; at week 20 – from 27 to 125 U/ml.

important Also, during an ultrasound, they measure, determine the degree of development of its organs and other indicators that are of great importance for identifying possible abnormalities.

Deviation from norms

After performing an ultrasound and receiving the results, the doctor not only compares the results obtained with standard values, but also calculates the degree of risk based on the likelihood of a particular pathology occurring.

Actual screening rates are divided by the average obtained by processing data from previous studies that included women of approximately the same age living in the area.

The result obtained is denoted by the abbreviation “MoM”.

If the MoM value is between 0.5 and 2.5, it is considered normal indicator. The closer the obtained result approaches one, the better the screening result.

The total result of the second screening is recorded as a fraction, for example, 1:500.

• If the denominator in this expression is greater than 380, this is a normal result (eg 1:400 or 1:1000).
• If the number in the denominator is less than 380(for example, the result is 1:290), then the likelihood of certain abnormalities in the fetus is quite high.
• If the obtained indicator is in the range from 1:250 to 1:360, it is advisable for the expectant mother to consult a geneticist.
• At risk level 1:100 It is recommended to carry out invasive diagnostics to determine the chromosome set of the fetus.

The expectant mother should remember that the probability of receiving a false positive screening result is about 10%, and a false negative one – up to 30%.

additionally You should not panic if the doctor reports the presence of some possible violations in the fetus. In this case, it is necessary to undergo additional types of examinations in order to clarify the data obtained.

It is very important to remain calm and confident when undergoing screening, because the level of hormones in the blood largely depends on a woman’s psychological mood.

After passing the second screening, you should also follow the doctor’s recommendations regarding lifestyle, physical activity, in order to increase the likelihood of having a healthy child.

Nowadays, doctors refer every pregnant woman for an ultrasound examination. The standard implies three ultrasound examinations, regardless of the presence of complaints, even if the fetus is assessed as healthy. So-called perinatal screenings include, in addition to ultrasound, a biochemical blood test of the expectant mother. Why is screening in the 2nd trimester necessary and what are the norms for ultrasound, at what period it is performed and for what - we will talk about this and more in this article.

Screening ultrasound is usually performed 3 times, since it is customary to divide the gestation period into 3 trimesters.

Who needs a second screening and why?

2 Ultrasound screening in our country is prescribed to every pregnant woman, regardless of the presence of complaints. But pregnant women at risk should be especially careful about the study. These include:

• primigravidas over 35 years of age;
• persons in closely related marriages;
• pregnant women with a burdened obstetric and gynecological history;
• parents suffering from alcoholism and drug addiction.

But all other expectant mothers should also act responsibly so as not to miss the occurrence of a pregnancy-threatening pathology at an early stage. The correspondence of the screening result and the ultrasound norm will allow the woman to feel calm, knowing that everything is fine with her and the child.

What indicators does 2nd trimester screening evaluate?

During an ultrasound scan of the second trimester, the sonologist will definitely pay attention to the correspondence of the size of the fetus (fetometric indicators) to the gestational age. There are also a number of special markers by which it is customary to judge the presence of anomalies and defects in a child.

The specialist evaluates, among other things:

• violation of the formation of the bones of the skull (nasal bone, bones of the hard palate);
• size and structure of the lungs, their maturity;
• state internal organs(for example, the formation of the cavities of the heart and blood flow in them);
• the presence of all fingers and toes (a change in their number indicates internal disorders).

Values ​​within the normal range for fetal ultrasound do not allow the doctor to complete the study. Additionally, it is necessary to assess the condition of the mother’s reproductive system, as this greatly affects the course of pregnancy. The degree of maturity of the placenta, the condition of the uterus and ovaries and the number amniotic fluid– important values ​​assessed in each of the 3 trimesters of pregnancy.

Decoding the ultrasound report

After the examination, the specialist must give the woman a conclusion. But for an ignorant person such data is hardly informative. Traditionally, a sonologist does not make a diagnosis, but refers the pregnant woman to a local gynecologist, who advises the patient on all issues of interest.

If the expectant mother has to wait several days for a consultation with the attending physician, she will certainly inquire about compliance with the norm in advance. It should be remembered that the doctor always judges the pathology only by the totality of fetometric indicators, and he is almost never alarmed by any one value.

Each child is individual even before birth. And if the expectant mother has really serious reasons for concern, then the ultrasound specialist will inform her about this immediately. Nevertheless, we will tell you about the main indicators of the second screening and their normal values.

Body length and fetal weight

At the beginning of the second trimester, the embryo is growing very actively, and it is difficult to judge the standards. On average, the length of the fetus increases from 10 to 16 cm during the twentieth week of pregnancy. Here it is important to take into account not the absolute figure in centimeters, but the increase in growth over the weeks.

If the specialist is alarmed by something, the pregnant woman will be offered a repeat examination after a week or two.

Fetometric indicators of the fetus

Fetal weight from ultrasound can only be determined using special formulas. Therefore, this value can be very inaccurate depending on the device, the doctor and the position of the baby in the womb. With a weight of about 300 grams, all the child’s organs are fully formed, and at about 450 grams, a baby born prematurely can survive. It seems incredible!

Abdominal and head circumference

Just like the baby's height, these important values ​​vary widely and should strictly correspond to the stage of pregnancy. There are often cases when “developmental delay” in practice turned out to be an incorrectly diagnosed gestational age. However, the widespread introduction of early ultrasound diagnostics has reduced the number of such errors.

Results of measuring the circumference of the head and abdomen of the fetus and their correspondence age norm are indicated in the table.

Norms for abdominal circumference and fetal head circumference in millimeters

Biparietal (BPR) and fronto-occipital (FOR) size of the fetal head

It is not surprising that all ultrasound diagnosis of pathologies during pregnancy is based on. It is unlikely that any human organ is comparable in complexity and importance to the brain. Normal ultrasound values ​​for these indicators are also presented in the table.

Table of norms of LZR and BPR

Deviations from reference values ​​may indicate the formation of serious fetal deformities, such as anencephaly or hydrocele. But as a rule, such diseases are judged by several repeated ultrasounds.

Length of bones: tibia, femur, humerus and forearm

Some deviation from the norms for weeks of pregnancy indicated in the table is acceptable and may be determined by individual characteristics. The doctor will be alerted by a sharp shortening of the entire limb or different lengths of arms or legs in one child.

Another numerical indicator that must be included in the ultrasound report due to its importance: amniotic index (AI). This index is obtained by measuring the distance from the fetal body to the uterine wall at three points, so that the probability of error is low. Despite the fact that possible fluctuations in this index are very wide, ranging from 70 to 300 mm, its excess or low levels can threaten the development of pregnancy and require emergency medical intervention.

Table with amniotic index indicators

Conclusion

Nowadays, ultrasound during pregnancy is an indispensable method for detecting pathologies in apparently healthy patients. It is distinguished by its absolute painlessness and wide availability. Thanks to the introduction of three mandatory perinatal screenings, it was possible to help many women and save many children. The article describes in detail at what stage and for what purpose screening is performed in the second trimester of pregnancy.

The second stage of the program of mass diagnostic screening (screening) of pregnant women to identify risk groups among them for pathologies of fetal development is biochemical screening of the 2nd trimester. The timing of a biochemical blood test is considered optimal from the 16th to the 18th week of pregnancy, and acceptable from the 14th to the 20th week.

Prenatal (antenatal) screening is a complex of non-invasive (safe) diagnostic methods. It is recommended for all pregnant women, approved by the Ministry of Health of the Russian Federation and includes: combined + biochemical screening test for the 2nd trimester. In accordance with international standards, the data from these studies is used by a computer system for the final integral calculation of the risks of congenital chromosomal and hereditary pathologies of the fetus.

Scheme of a comprehensive prenatal screening program

Combined screening of the 1st trimester reveals up to 95% of cases of Down syndrome (trisomy syndrome +21 chromosomes) and Edwards syndrome (trisomy syndrome +18 chromosomes), and also makes it possible to suspect other chromosomal abnormalities based on the condition of the abdominal wall and the head of the fetal neural tube.

Screening carried out in the optimal period of the 2nd trimester is less informative in terms of detecting Down and Edwards syndromes - no more than 70% of cases. Its main goal is to confirm/exclude neural tube defects and other pathologies of fetal development and to calculate the associated risks of the following congenital chromosomal and hereditary diseases:
- Patau syndrome - syndrome of trisomy +13 chromosomes or chromosomal group D (13-15 chromosomes),
- Shershevsky-Turner syndrome (hereditary),
- Carnelia de Lange syndrome (hereditary),
- Smith-Opitz syndrome (hereditary),
- polyploidy (triploid set of chromosomes in the fetus).

In recent years, after the introduction of early and more informative combined prenatal screening of the 1st trimester, screening of the 2nd trimester is used to a limited extent, at the request of the patient.

1. Late registration of a pregnant woman when the combined prenatal screening of the 1st trimester is missed.
2. Controversial/unsatisfactory results of the first screening.
3. For medical reasons.
4. Family history of congenital pathologies.
5. Spontaneous miscarriages on early stages the patient's history of pregnancy.

What you need to know about 2nd trimester screening

• During the period from the 16th to the 18th week of pregnancy, a screening program evaluates only biochemical blood parameters mother.
• The patient should have with her the results of the first combined screening or an ultrasound report, where indicated exact gestational age.
• Before donating blood, you should fill out a second screening questionnaire. It must indicate ultrasound markers 1st trimester screening(KTR, TVP, ...).
• Blood is drawn from a vein in the morning, strictly on an empty stomach.

Markers of biochemical screening tests 2nd trimester

Norms - reference values ​​- of biochemical markers in different laboratories are not the same(various equipment, research methods, units of measurement, etc.). They are indicated on the form with the results of blood tests in each specific case.

Normal limits for all biochemical markers in MoM are the same: 0,5 – 2,0

• MoM is the ratio of the patient’s biochemical marker value to the median (the average value of this marker for given period pregnancy)

AFP - α-fetoprotein

A specific protein produced by the embryo itself. AFP is a marker of congenital malformations of the fetus. It is detected in amniotic fluid already at the 6th week of pregnancy; by the 16th week, AFP reaches its diagnostic level in the mother’s blood and in some cases makes it possible to detect neural tube defects and other pathologies of fetal development.

It should be noted that often “abnormal” AFP test results as part of 2nd trimester screening are explained by an incorrectly determined gestational age, multiple or large pregnancy, but not by pathology of fetal development.

HCG – human chorionic gonadotropin

Gonadotropic hormone, hCG is detected in a woman’s urine already on the 5-7th day of pregnancy - it is he who “demonstrates” the second line of the pregnancy test. In the early stages, hCG is produced by the membranes of the fetal embryo, and later by the placenta. HCG is a marker of pregnancy well-being; its content in the mother’s blood changes precisely in accordance with the duration of pregnancy.

E3 - free estriol

An inactive female sex hormone, outside of pregnancy, is detected in human blood in low concentrations. In the early stages of pregnancy, it is intensively produced by the placental apparatus, and later by the fetus itself. The level of free estriol in a woman’s blood increases in accordance with the length of her pregnancy. Its critical decrease/increase allows one to suspect pathology in the course of pregnancy and fetal development.

An example of the interpretation of a “triple” biochemical test performed during the 2nd trimester screening period

Inhibin A

During pregnancy, the placenta becomes the main producer of this protein. Inhibin A is an early marker of pregnancy termination; its decrease by ˂0.5 MoM indicates a threat of miscarriage. The level of inhibin A in the blood of women with recurrent miscarriage is several times lower than in patients with normal pregnancy.

Studying the level of inhibin A in the 2nd trimester of pregnancy (the “quadruple” screening test) and introducing these results into the integral test makes it possible to calculate the risks of Down syndrome with the greatest accuracy. An increase in inhibin A in the second trimester indicates a dysfunction of the placenta.

The importance of prenatal screening in the 2nd trimester. High risks - what to do?

The conclusion of the screening program about a high risk of 1: 250 or higher for any chromosomal or congenital pathologies of the fetus is not a final diagnosis, but a good reason for consulting a geneticist. If the risk is 1:100, invasive (unsafe) methods for diagnosing chromosomal abnormalities of the fetus are recommended for pregnant women:

• Amniocentesis is the collection of genetic material (DNA) of the fetus from amniotic (amniotic) fluid.
• Cordocentesis is the collection of umbilical cord (cord) blood from the fetus. It is carried out after 18-20 weeks of pregnancy.

Only DNA testing (karyotyping) of an unborn child can give a 99% accurate answer about the presence/absence of chromosomal diseases.

The fact that individual fetal cells of the fetus penetrate the placenta into the maternal bloodstream has long been known. As laboratories are equipped with modern equipment and the qualifications of medical staff are improved, prenatal screening of the 2nd trimester is being replaced by a non-invasive prenatal test (NIPT = microarray analysis = molecular cytogenetic analysis = blood for DNA). NIPT is the diagnosis of chromosomal abnormalities using fetal cells taken from the mother’s blood after 8 weeks of gestation. However, conducting a “quadruple” test to detect other pathologies during pregnancy is and will remain relevant.

Prenatal screening of the 2nd trimester in its timing does not exclude the receipt of false-positive/false-negative results of the integral screening test. Do not try to interpret the risks yourself - consult a doctor for medical genetic consultation.
HEALTH TO THE MOTHER AND HER BABY!

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