Ultrasound of pregnant women 2 screening. Biochemical laboratory research. Neural tube defect

13.06.2019

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. The so-called perinatal screenings include, in addition to ultrasound, a biochemical blood test of the expectant mother. Why is screening of the 2nd trimester needed and what are the standards for ultrasound, for how long it is performed and why - we will talk about this and other in this article.

Screening ultrasound is usually performed 3 times, since it is customary to divide the gestational age 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 you should be especially careful about the study of pregnant women from risk groups. These include:

primary pregnant women over 35 years old;
persons who are in a closely related marriage;
pregnant women with a burdened obstetric and gynecological history;
parents suffering from alcoholism and drug addiction.

But all other expectant mothers should be treated responsibly so as not to miss the emergence of a pathology threatening pregnancy at an early stage. The conformity of the screening result and the ultrasound rate will allow the woman to feel calm, realizing that everything is in order with her and the child.

What indicators does the 2nd trimester screening measure?

During the ultrasound of the second trimester, the sonologist will definitely pay attention to the correspondence of the size of the fetus (fetometric parameters) 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, among other things, assesses:

violation of the formation of the bones of the skull (nasal bone, bones of the hard palate);
the size and structure of the lungs, their maturity;
the condition of the internal organs (for example, the formation of heart cavities 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 state of the mother's reproductive system, as this greatly affects the course of pregnancy. The degree of maturity of the placenta, the state of the uterus and ovaries and the amount of amniotic fluid are important values assessed in each of the 3 trimesters of pregnancy.

Deciphering the conclusion of the ultrasound

After the study, the specialist must issue a conclusion to the woman. But for an uninformed person, such data is hardly informative. Traditionally, the sonologist does not make a diagnosis, but directs the pregnant woman to the 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 fetometry indicators, and almost never he is alarmed by any one value.

Every child is different even before birth. And if the expectant mother has really serious reasons for concern, then the ultrasound specialist will inform her about it immediately. Still, let's talk 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 grows from 10 to 16 cm and the twentieth week of pregnancy. Here it is important to take into account not the absolute figure in centimeters, but the increase in growth by week.

If the specialist is alerted to something, the pregnant woman will be offered a second examination after a week or two.

Fetometric indicators of the fetus

Fetal weight by 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 organs of the child are fully formed, and approximately 450 grams of a premature baby can survive. It seems incredible!

Circumference of the abdomen and head

As well as the height of the baby, these important values vary widely and must strictly correspond to the gestational age. There are frequent 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.

The results of measuring the circumference of the head and abdomen of the fetus and their compliance with the age norm are shown in the table.

Norms of abdominal circumference and fetal head circumference in millimeters

Biparietal (BPD) and fronto-occipital (LZR) size of the fetal head

It is not surprising that all ultrasound diagnostics of pathologies during pregnancy is based on. It is unlikely that at least one 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 LZR and BPR norms

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

Bone length: lower leg, femur, humerus and forearm

Some deviation from the norms indicated in the table by weeks of pregnancy is permissible, 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 conclusion of an ultrasound scan because of its importance: the amniotic index (AI). This index is obtained by measuring the distance from the body of the fetus to the wall of the uterus at three points, so that the probability of error is low. Despite the fact that the possible fluctuations of this index are very wide in the range from 70 to 300 mm, its exceeding or low values can threaten the development of pregnancy and require urgent medical intervention.

Amniotic Index Table

Conclusion

Nowadays, ultrasound during pregnancy is an indispensable method for detecting pathologies in apparently healthy patients. It is distinguished by absolute painlessness and wide availability. Thanks to the introduction of three mandatory perinatal screenings, many women have been helped and many children have been saved. The article describes in detail for how long and for what purpose the screening of the second trimester of pregnancy is performed.

Deciphering the results of the 2nd trimester screening procedures helps to identify the occurrence of the risk of having an infant with a chromosomal disease, with a neural tube defect or other pathology.

Screening of the 2nd trimester is also an opportune moment to examine the level of fetal hormones, in particular those of the liver and placenta, due to which it is possible to obtain detailed data on the development of the unborn baby.

Perinatal screening of the second trimester - the decoding of this incomprehensible name for expectant mothers may sound simpler: a comprehensive examination of the fetus with the possibility of detecting pathologies at the genetic and chromosomal level.

A second screening is prescribed during the second trimester of pregnancy.

But, despite the fact that the ideal period for passing it is 16 - 18 weeks, expectant mothers can go through it, starting from 14 weeks of gestation to 20.

This type of comprehensive examination necessarily consists of an ultrasound scan (if necessary with a Doppler) and a triple biochemical screening test.

Screening of the 2nd trimester is considered an additional examination. If the doctor leading the pregnancy sees that the position of the expectant mother is normal, a second screening may not be necessary.

In most cases, this complex procedure is carried out on a paid basis, but this does not reduce the number of those wishing to undergo 2 screening and receive confirmation that their unborn child is healthy.

At the first stage, an ultrasound scan is performed. Deciphering its results allows you to obtain information about the general condition of the unborn child and to clarify the duration of pregnancy.

If, during the ultrasound scan, the doctor revealed abnormalities in the development of the fetus, then the pregnant woman is prescribed an ultrasound scan with a Doppler.

This type of procedure allows you to judge the patency of blood vessels. This method examines the uteroplacental blood flow, the blood flow of the umbilical arteries, as well as the blood flow of the fetal brain.

At the same time, experienced specialists argue that in order to obtain an accurate diagnosis of a deviation from the norm, a pregnant woman must undergo an ultrasound scan with a Doppler twice, the second time after two weeks, and best of all on another device.

After the ultrasound of the second trimester, on the same day, a biochemical blood test is done.

A pregnant woman donates blood from a vein for a "triple test", the results of which make it possible to determine the level of the following substances in the blood:

HCG (chorionic gonadotropin) is a hormone. Present only in pregnant women. It is hCG that allows you to find out about the onset of pregnancy using a home express test;
AFP (alpha-fetoprotein) is a protein. In the required amount, it provides protection to the developing infant from the risk of a threat from maternal immunity;
NE (free, unbound or unconjugated estriol) is a steroid hormone. The main estrogen that contributes to the normal metabolism between two organisms - mother and child.

Interpretation of the results of ultrasound of the second screening

Since a routine ultrasound examination of the second trimester can call into question the normal development of the fetus, the expectant mother is prescribed an ultrasound scan with a Doppler.

The procedure does not require special preparation, therefore, Doppler or Doppler ultrasonography can be performed at any convenient time.

Doppler ultrasound and Doppler ultrasound are both procedures that assess blood flow.

All data are visualized on the screen in the form of a graphic and color image of the velocity curves, only during Doppler sonography is the record recorded on the tape, which makes it possible to control the change in blood flow for a better or worse side after treatment.

Deciphering the results of a second trimester ultrasound with Doppler may be as follows:

assessment of the blood flow of the uterine vessels;
assessment of the umbilical arteries;
assessment of the middle vessel of the fetal brain.

Assessment of the state of the uterine vessels is carried out using IR (resistance index).

The specialist determines the state of blood flow in the right and left arteries of the uterus, when assessing only one of them, the results are false and far from normal, which can subsequently seriously harm the mother and her baby.

This fact is explained by the fact that with gestosis (toxicosis), blood flow is disturbed only in one artery.

On this score, there is the following theory: if the blood flow is disturbed in the right vessel of the uterus, it means that the expectant mother may have toxicosis in the third trimester of pregnancy.

Very often, late gestosis is accompanied by negative consequences. At 20 weeks, the mean IR of the uterine vessels may be 0.52; permissible IR is 0.37 - 0.70.

The examination of the vessels of the umbilical cord is performed under two conditions: first, the fetus is in a calm state; the second - the heart rate is 120 - 160 beats / min.

This fact is due to the fact that if the heart rate results deviate from the required norms, there is a decrease or increase in the resistance index in the umbilical cord arteries.

The umbilical cord has three main blood vessels: 1 vein and 2 arteries. The purpose of ultrasound is to identify a possible abnormality in the form of 1 artery and 1 vein.

In this case, the fetus will experience a lack of oxygen and nutrition, which will negatively affect the growth and development of the unborn child.

In specific cases, the fetus adapts to such conditions, as a result, healthy babies are born, but with low weight.

If one vessel is functioning, in which the blood flow is disturbed, one should not hope for a positive outcome of gestation and childbirth.

A pregnant woman urgently needs to undergo an expert ultrasound examination in the direction of a doctor and donate blood for chromosomal abnormalities.

The pathology of the middle artery of the brain makes the unborn baby suffer: his poor health is determined by the level of decrease in PI (pulsation index) in the vessels of the brain.

If a child has a hemorrhage in the skull, then there is an increase in IR in the arteries of the brain. At the 20th week of pregnancy, the average PI rate in the cerebral artery is 1.83; the allowable figure is 1.36 - 2.31.

Explanation of the results of the "triple screening test"

Receiving the results of a blood test from a vein, specialists compare them with the established norms of the current trimester, on the basis of which they judge the course of pregnancy and the state of health of the unborn child.

HCG rates of the second screening at term:

16 weeks: 10,000 - 58,000 ng / ml;
17-18 weeks: 8,000 - 57,000 ng / ml;
19 weeks: 7,000 - 49,000 ng / ml.

Minor deviations of hCG from the norm during the second trimester screening are not of diagnostic value.

If a biochemical analysis revealed an increased level of hCG, then this fact may indicate multiple pregnancies.

In this case, conducting a "triple screening test" does not make sense at all, since all the results will be overestimated.

Also, the reason for the increase in this hormone in the blood can be reduced to the presence of a chromosomal abnormality of the fetus or diabetes mellitus in a pregnant woman.

If a biochemical analysis reveals a low level of hCG in the second trimester of pregnancy, this may be a symptom of a chromosomal abnormality or a missed pregnancy.

AFP (alpha-fetoprotein) norms for the term:

12-14 weeks: 15-60 units / ml;
15 - 19 weeks: 15 - 95 units / ml;
20 weeks: 27 - 125 units / ml.

The deviation of AFP from the norm in the form of a decrease in protein production in the gastrointestinal tract and liver of the fetus suggests the development of Down's or Edwards syndrome, as well as the incorrectly indicated gestational age.

An increased level of AFP is considered a sign of pathology in the development of a neural tube, cranial or umbilical hernia, liver necrosis caused by a viral infection.

Norms of NE (free estriol) for the term:

13-14 weeks: 5.7 - 15 ng / ml;
15-16 weeks: 5.4 - 21 ng / ml;
17-18 weeks: 6.6 - 25 ng / ml;
19-20 weeks: 7.5 - 28 ng / ml;

If a biochemical screening test reveals a deviation of NE from the norm in the form of an increase in its level in the blood of a pregnant woman, then this may be a symptom of multiple pregnancy, a large fetus, or liver dysfunction.

If the biochemical test determined a decrease in NE, then the possible reason lies in the intake of antibiotics, infection of the fetus, developmental pathology or in placental insufficiency.

But even if the biochemical analysis shows a deviation of estriol from the desired results, it is not worth taking this fact without additional research as a direct indication of the presence of pathology in the fetus.

Only by the totality of the results and by comparing the indicators of all analyzes in dynamics it will be possible to judge the consequences.

The second screening during pregnancy is carried out in order to identify congenital defects and chromosomal abnormalities that could not be detected at stage 1 of the examination in the previous trimester. The complex of studies includes ultrasound and a biochemical blood test of the expectant mother. What are the weeks of screening in the 2nd trimester? How to prepare for it, how to take it and what does it show?

Features of the second screening

During pregnancy, there are 3 screenings, one in each trimester. If the blood counts in the initial trimester of pregnancy were normal, stage 2 usually consists only of a planned ultrasound scan. However, if a woman is at risk, she needs to undergo the second screening in full. A pregnant woman is referred to this category if:

had problems carrying a child in previous pregnancies;
have had a severe infection during the current pregnancy;
future parents are consanguineous;
the first screening revealed a high risk of congenital abnormalities;
age over 35;
there is a long-term threat of miscarriage;
used medications prohibited during gestation;
future mothers and fathers, their older children have congenital diseases or developmental defects;
neoplasms were found.

How long does it take?

This article tells about typical ways of solving your questions, but each case is unique! If you want to know from me how to solve your particular problem - ask your question. It's fast and free!

The timing of the examination can vary from 16 to 24 weeks of pregnancy. There are some peculiarities here. The results of a blood test are considered the most accurate if the biomaterial was taken from 16 to 18 weeks. The terms of the ultrasound scan, according to the order of the Ministry of Health, are from 18 to 21 weeks. Most often, in practice, the timing of the second screening is from 18 to 20 weeks. The exact date of the examination is determined by the doctor conducting the pregnancy.

What are they watching?

With the help of ultrasound of the 2nd trimester, which is often done for a period of 20 weeks, the anatomical structure of the fetus is assessed for developmental anomalies and signs of hereditary diseases. The state and volume of amniotic fluid, fetal heartbeat, and its mobility are determined. They look at the parameters of the baby's body: the length of the bones of the upper and lower extremities, height, size of the head and abdomen.

An ultrasound scan determines the formation and location of the placenta, the number of vessels in it. The doctor also assesses the condition of the uterus, cervix and ovaries, the tone of the uterine walls.

The specialist checks the number of fingers, size, structure and maturity of the baby's organs. The structure of his facial bones, nose and hard palate is assessed.

As part of a prescription screening, blood parameters such as alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG) are assessed. AFP is a protein produced by the fetus. It transfers the necessary compounds to all organs and tissues of the baby, protects it from the maternal immune system, and neutralizes estrogens. HCG is produced by the membranes of the fetus. It stimulates the synthesis of other hormones glucocorticoids and progesterone, supports the functioning of the placenta.

How is the research done?

Ultrasound examination of the second trimester does not require special preparation, however, the day before the procedure, it is recommended to refrain from fried and fatty foods, chocolate, citrus fruits, cocoa. Blood is taken on an empty stomach, so it is better to prescribe an analysis in the morning. It is recommended to give up water a couple of hours before the test. If the pregnant woman is taking any medications, they may be postponed by the doctor's decision.

For an ultrasound scan, the expectant mother lies down on the couch and exposes her belly. The procedure in the 2nd trimester is done transabdominally. A special gel is applied to the skin, which acts as a conductor between the device and the body. The transducer sends out sound waves that are reflected off the tissue and returned back. The signals are converted and displayed on the monitor screen, where the image is rendered. The specialist moves the sensor over the abdomen, takes the necessary measurements and records the information received. The procedure takes from 15 to 25 minutes, the result is given immediately.

Norms and interpretation of results

Table. Second planned ultrasound, norms:

Gestational age	Abdominal circumference	Head circumference	Frontal-occipital size, mm	Biparietal size (head width), mm	Forearm bone, mm	Femur, mm	Humerus, mm	Leg length, mm	Nose bones	Amniotic index
16	88–116	112–136	41–49	31–37	12–18	17–23	15–21	15–21	5,4–7,2	73–201
17	93–131	121–149	46–54	34–42	15–21	20–28	17–25	17–25	5,4–7,2	77–211
18	104–144	131–161	49–59	37–47	17–23	23–31	20–28	20–28	6,6–8,0	80–220
19	114–134	142–174	53–63	41–49	20–26	26–34	23–31	23–31	6,6–8,0	83–225
20	124-144	154–186	56–68	43–53	22–29	29–37	26–34	26–34	7,0–8,3	86–230
21	137–177	166–200	60–72	46–56	24–32	29–37	29–37	29–37	7,0–8,3	88–233

Table. Second screening, normal blood counts:

The second screening helps to identify abnormalities in blood counts, which may indicate abnormalities in the course of pregnancy and fetal malformations. Decryption is carried out by a doctor; if suspicious results are detected, the test is repeated. If you wish, you can take the screening test 2 times in a row - it is absolutely safe.

The reasons for the increased hCG can be: excess weight of the expectant mother, gestational diabetes mellitus, artificial insemination, multiple pregnancies. On the part of the fetus, the deviation can be caused by defects and genetic abnormalities. The indicator is reduced if there is a threat of miscarriage and miscarriage, there is placental insufficiency or developmental delay.

An increase in alpha-fetoprotein indicates multiple pregnancy or a malformation of the brain - anencephaly. Another pathology that causes such a deviation is a genetic anomaly of the spinal column, in most cases accompanied by impaired development of the spinal cord, more often in the form of a spinal hernia. A low indicator may indicate chromosomal abnormalities - Edwards or Down syndrome.

Why is a triple test needed in the 2nd trimester and how is it carried out?

A triple test is a set of studies that includes 3 analyzes. They also help assess the health of the baby. Such a test is prescribed in addition to the mandatory second ultrasound. In addition to the hCG and AFP indicators, the level of free estriol is assessed - this is a hormone that is responsible for establishing the relationship between the mother and the fetus. It is produced by the placenta, and later by the baby's liver. He takes part in the placental circulation, the production of progesterone, the preparation of the mammary glands for lactation.

For biochemical screening of the 2nd trimester, the biomaterial is taken from a vein, usually an ulnar one. A tourniquet is applied 10 cm above the elbow. After they ask the pregnant woman to clench and unclench her fist several times to enhance blood flow. The health worker determines the puncture site, disinfects and makes a fence. After that, a sterile napkin is applied. In order to stop bleeding and prevent bruising, the arm should be kept bent at the elbow for about 10 minutes. The analysis is performed using a computer, the result is prepared up to 14 days.

Normal estriol results in the second screening (triple test) are given in the table:

High levels of free estriol are observed with multiple pregnancies and an increased level of oxytocin in the body of the expectant mother. Low values may indicate complications: chromosomal abnormalities, hypoxia, fetal freezing, growth retardation, placental insufficiency. Possible reasons for the downward deviation: diabetes mellitus, liver disease and anemia.

Quadruple test - what is it and why is it done?

The quadruple test, which is also carried out as part of the second screening, includes the same blood tests as the triple, but one more indicator is added to them - inhibin A. This is a sex hormone that is always present in the body, but its level rises during pregnancy ...

It is a marker of chromosomal abnormalities (Down and Edwards syndromes), therefore its value is used to assess the risk of such congenital anomalies. The upper threshold is 2 MoM, an excess indicates a deviation. Low levels of inhibin A occur with recurrent miscarriage or other abnormalities in the course of pregnancy.

How much does screening cost?

Screening for the 2nd trimester costs differently depending on where the study is being conducted. In state institutions, ultrasound can be taken free of charge, however, a biochemical test under such conditions is available only to pregnant women at risk. Commercial clinics set prices based on the quality of service, equipment and location (in large cities, the cost is usually higher).

The price is influenced by the range of services to be done. A double screening (blood test) is cheaper than triple or quadruple screening.

Biochemical screening, depending on the number of assessed indicators, costs 1000–2000 rubles in Moscow. (data as of September 2018).

Description

Study material Blood serum

The study is performed for screening of pregnant women in order to assess the risk of fetal chromosomal abnormalities - trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), as well as neural tube defect (NTD). Research results are quantified using PRISCA software.

Attention! This study requires the presence of ultrasound results!

Biochemical screening of the second trimester of pregnancy "triple test" of the second trimester consists of the following studies:

Human chorionic gonadotropin (hCG, beta-hCG, b-hCG, Human Chorionic gonadotropin, HCG), test No. 66;

Alpha-fetoprotein (AFP, a-Fetoprotein), test No. 92;

Free estriol (unconjugated estriol), test No. 134.

Determination of the concentration of these markers is used for screening of pregnant women in the second trimester of pregnancy in order to assess the risk of chromosomal abnormalities and fetal neural tube defect. The study is carried out between 15 and 20 weeks of gestation. The optimal timing for screening for the 2nd trimester is from 16 to 18 weeks of pregnancy.

Conducting a comprehensive examination at 11-14 weeks of pregnancy, including performing an ultrasound scan and determining maternal serum markers (free beta subunit of hCG and PAPP-A), followed by a comprehensive software calculation of the individual risk of having a child with chromosomal pathology, is recommended for all pregnant women by order of the Ministry of Health RF of "01" November 2012 No. 572n ("Procedure for the provision of medical care in the profile of" obstetrics and gynecology "). With normal 1st trimester screening results, a separate AFP test can be used in the 2nd trimester to rule out a neural tube defect (see AFP test # 92), or the complete 2nd trimester PRISCA profile can be used. A triple biochemical test with a comprehensive software calculation of risks in the 2nd trimester may be especially appropriate in case of borderline risk assessment results during screening of the 1st trimester, and also if, for some reason, screening of the 1st trimester was not carried out on time.

The PRISCA program (developed by Typolog Software, distributed by Siemens) is a program certified in the European Union (CE-certification) and registered for use in the Russian Federation, which supports the calculation of risks during screening examinations of the 1st and 2nd trimesters of pregnancy. The calculation of risks is carried out using a combination of biochemical markers and ultrasound indicators that are informative for the corresponding period. Ultrasound data of the 1st trimester, performed for a period of 11-13 weeks, can be used to calculate the risks in the PRISCA program during biochemical screening of the 2nd trimester. At the same time, the PRISCA program will carry out an integrated calculation of risks taking into account the value of TVP (thickness of the fetal collar space) relative to the median values of this indicator for the gestational age on the date of its measurement in the 1st trimester.

For correct calculations, the accuracy of the specified individual data, the qualifications of the doctor conducting the ultrasound in performing measurements of prenatal screening ultrasound, as well as the quality of laboratory tests are extremely important.

Preparation

It is preferable to take blood in the morning on an empty stomach, after 8-14 hours of the night fasting period (you can drink water), it is permissible in the afternoon after 4 hours after a light meal.

On the eve of the study, it is necessary to exclude increased psychoemotional and physical activity (sports training), alcohol intake, and an hour before the study - smoking.

Screening for the first trimester is optimal at 11-13 weeks, for the second trimester at 16-18 weeks. Ultrasound data of the first trimester can be used to calculate the risk during biochemical screening of the second trimester.

Indications for appointment

Screening examination of pregnant women in the second trimester of pregnancy to assess the risk of chromosomal abnormalities and fetal neural tube defect, especially useful in case of borderline results of the estimated risk of chromosomal abnormalities in the 1st trimester screening, and also if the 1st trimester screening examination was not carried out on time.

To complete the study, you must fill in.

Interpretation of results

Interpretation of test results contains information for the attending physician and does not constitute a diagnosis. The information in this section cannot be used for self-diagnosis and self-medication. An accurate diagnosis is made by a doctor using both the results of this examination and the necessary information from other sources: anamnesis, results of other examinations, etc.

The survey results are issued in the form of a report form. It indicates the data used in the calculations, the results of the studies carried out, the corrected MoM values. In the conclusion, quantitative indicators of the degree of risk for trisomy 21 (Down's syndrome), trisomy 18 (Edwards syndrome) and neural tube defect (NTD) are indicated, which reflect the frequency of occurrence of the corresponding types of pathology with similar results of examinations and individual data. For example, a risk index of 1: 6250 means that the statistical probability of having a child with the corresponding pathology is one case in 6250 pregnancies with similar individual data. The PRISCA program has established conditional thresholds for identifying a high-risk group - the frequency is higher than 1/250 for trisomy 21 (Down's syndrome), higher than 1/100 - for trisomy 18, AFP MoM above 2.5 - for a neural tube defect.

The results of calculating the risk of fetal chromosomal abnormalities based on screening biochemical studies and ultrasound indicators are only statistical probabilistic indicators that are not a basis for a diagnosis, but may serve as an indication for the appointment of further special research methods. According to the current recommendations of the Ministry of Health of the Russian Federation, when a pregnant woman is found to have a high estimated risk for chromosomal abnormalities in the fetus (individual risk 1/100 and higher), the obstetrician-gynecologist sends her to a medical genetic consultation (center) for medical genetic counseling and or confirming the diagnosis using invasive examination methods to establish the karyotype of the fetus.

The use of complex (ultrasound + biochemical) screening, according to a number of studies, makes it possible to detect Down syndrome in a fetus of pregnancy in 85 - 90% of cases with 5% of false-positive results. Comprehensive screening helps to identify not only the risk of a fetal chromosomal abnormality, but also the overall risk of pregnancy pathology.

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

Prenatal (antenatal) screening is a set 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 are used by the computer system for the final integral calculation of the risks of congenital chromosomal and hereditary fetal pathologies.

Scheme for a comprehensive prenatal screening program

/ indicated the optimal timing and tests /

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

Screening of the 2nd trimester, carried out at the optimal time, 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, other pathologies of fetal development and calculate the associated risks of the following congenital chromosomal and hereditary diseases:
- Patau syndrome - trisomy syndrome +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 an earlier 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.

In what cases is it strictly necessary to conduct biochemical screening in the 2nd trimester of pregnancy?

1. Late registration of a pregnant woman, when the combined antenatal screening of the 1st trimester is missed.
2. Controversial / unsatisfactory results of the first screening.
3. For medical reasons.
4. Complicated family history of congenital abnormalities.
5. Spontaneous miscarriages in early pregnancy in the patient's history.

What you need to know about 2nd trimester screening

From the 16th to the 18th week of pregnancy, the 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 it is indicated exact gestational age.
Before donating blood, you should fill out a second screening questionnaire. It must indicate the markers of the ultrasound 1 trimester screening(KTR, TVP, ...).
Blood is drawn from a vein in the morning, strictly on an empty stomach.

2 trimester biochemical screening test markers

Norms - reference values - biochemical markers are not the same in different laboratories(different equipment, research methods, units of measurement, etc.). They are listed on the case-by-case blood test form.

The normal range 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 a given gestational age)

AFP - α-fetoprotein

A specific protein produced by the embryo itself. AFP is a marker of congenital fetal malformations. It is determined in the amniotic fluid as early as the 6th week of pregnancy, by the 16th week, AFP reaches its diagnostic level in the mother's blood and in some cases allows the detection of neural tube defects and other pathologies of fetal development.

Interpretation of AFP indicators during pregnancy

It should be noted that often the "abnormal" AFP test results in the framework of the 2nd trimester screening are explained by the incorrectly determined gestational age, multiple or large-fetal pregnancies, but not by the pathology of fetal development.

HCG - human chorionic gonadotropin

The gonadotropic hormone, in the urine of a woman, hCG is determined already on the 5-7th day of pregnancy - it "manifests" the second strip 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 the well-being of pregnancy, its content in the mother's blood changes exactly in accordance with the gestational age.

E3 - Free Estriol

An inactive female sex hormone, outside of pregnancy is determined in human blood in small 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 the woman's blood increases in accordance with the increase in the duration of her pregnancy. Its critical decrease / increase allows one to suspect the pathology of the course of pregnancy and fetal development.

Interpreting E3 dynamics during pregnancy

An example of the interpretation of a "triple" biochemical test carried out at the time of screening of the 2nd trimester

Inhibin A

During pregnancy, the placenta becomes the main producer of this protein. Inhibin A is an early marker for stopping pregnancy, its decrease ˂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.

The study of inhibin A levels in the 2nd trimester of pregnancy ("quadruple" screening test) and the introduction of 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.

Significance of 2nd trimester prenatal screening. High risks - what to do?

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

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

Only a DNA study (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 cross the placenta into the maternal bloodstream has been known for a long time. As the laboratories are equipped with modern equipment and the qualifications of the medical staff are upgraded, prenatal screening of the 2nd trimester is replaced by a non-invasive prenatal test (NIPT = microarray analysis = molecular cytogenetic analysis = blood for DNA). NIPT - diagnosis of chromosomal abnormalities in fetal cells taken from the mother's blood after 8 weeks of gestation. However, conducting a "quadruple" test to detect other pathologies of the course of pregnancy is and will be 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 on your own - consult your doctor for medical genetic counseling.
HEALTH TO MOM AND HER BABY!

Save the article to yourself!

VKontakte Google+ Twitter Facebook Class! To bookmarks