What is prenatal screening and why is it needed? Screening of the first trimester of pregnancy - what you need to know about the norms and results Do perinatal screening

Introduction. Numerous studies have shown that in some conditions during pregnancy and fetal abnormalities, individual ultrasound and laboratory indicators of expectant mothers differ from the average. These indicators were combined into groups called prenatal screening, carried out in the first, second and third trimesters of pregnancy.

Prenatal screening is a complex of safe medical studies (laboratory [biochemical] and ultrasound) aimed at identifying a risk group for the development of fetal malformations during pregnancy (“prenatal” means “prenatal”, “screening” - “screening”). Prenatal screening is recommended ! to all pregnant women.

Before proceeding to further reading of the article, I recommend that you read the article Laboratory diagnosis of congenital fetal anomalies

With the help of prenatal screening, groups of patients are identified who have a higher risk of developing fetal malformations than others (high-risk groups). High-risk groups are such groups of patients, among whom there is a high probability of detecting a particular pathology. If a woman, as a result of the examination, is at risk, this does not mean that this pathology will necessarily develop. This only means that in this patient one or another type of pathology may occur with a greater probability than in other women.

Thus, the risk group is not identical to the diagnosis. A woman may be at risk, but there may not be any problems during pregnancy. Conversely, a woman may not be at risk, but she may have a problem.

Prenatal screening identifies a risk group for the development of the following conditions:

Some types of congenital malformations in the fetus are quite common, for example, Down's syndrome (trisomy 21 or trisomy 21). This disease, as well as some other congenital diseases, occurs at the moment of conception or at the earliest stages of embryonic development, and with the help of invasive methods of prenatal diagnosis (chorionic villus biopsy and amniocentesis) can be diagnosed at a fairly early stage of pregnancy. However, such methods are associated with a risk of a number of pregnancy complications: miscarriage, infection of the fetus, development of hearing loss in a child, etc. In particular, the risk of miscarriage after such studies is 1:200. Therefore, these studies are prescribed only for women of high risk groups after appropriate diagnostic examinations (prenatal screening) and consultations with medical specialists. Risk groups include women over 35 and especially over 40, as well as patients with the birth of children with malformations in the past. However, children with Down syndrome can also be born to very young women.

Depending on the research, there are the following types of prenatal screening (the risk of malformations in the fetus):

Effective detection of chromosomal abnormalities and congenital malformations of the fetus is possible only with the proper organization of all prenatal screening activities. At the same time, the main component of success is the centralization of laboratory research and the expert level of ultrasound performed by doctors with proven competence (FMF certificate) with a mandatory annual audit. Despite the fact that ultrasound is of great importance in the prenatal diagnosis of chromosomal abnormalities, its (ultrasound) effectiveness depends on many subjective factors, while the biochemical method is more objective and contributes to a reliable risk assessment. Ultrasound screening machines should be of the highest quality with all certified image archiving and replay software to standardize ultrasound as a verification method for prenatal diagnosis.

The general trend in the development of prenatal screening is the desire to obtain reliable information about the risk of developing certain disorders as early as possible in pregnancy. Therefore, combined screening at the end of the first trimester of pregnancy (terms of 11-13 weeks) makes it possible to approach the effectiveness of classical biochemical screening of the second trimester of pregnancy.

To increase the effectiveness of prenatal screening, screening of pregnant women is organized by levels. At the 1st level, a screening examination of pregnant women is carried out using biochemical genetic screening of serum markers in the 1st and 2nd trimesters of pregnancy, ultrasound screening, which makes it possible to form risk groups for possible genetic disorders of the fetus with a high probability. If abnormalities in biochemical or ultrasound markers are detected, the pregnant woman is referred to the second level of prenatal screening (see below). At the 2nd level of prenatal screening, bypassing the 1st, pregnant women are sent (immediately at the first appearance):

FIRST STAGE (LEVEL 1) prenatal screening is carried out in the period of 10 - 14 weeks of pregnancy and includes:

down syndrome

double biochemical test (optimally at 10-11 weeks): blood sampling from pregnant women for markers of congenital pathology in the fetus, namely PAPP-A [ PAPP-A] (plasma albumin associated with pregnancy, pregnancy associated plasma protein A) and beta-hCG (free beta subunit of human chorionic gonadotropin); using a double test in the first trimester, the risk of detecting Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18) in the fetus is calculated; the risk of neural tube defects cannot be calculated using a double test, since the key indicator for determining this risk is β-fetoprotein, which begins to be determined in the blood in the required concentrations only from the second trimester of pregnancy; special computer programs allow you to calculate the combined risk of fetal anomalies, taking into account biochemical parameters determined in the first trimester double test, the results of an ultrasound scan done at 11-13 weeks of pregnancy, weight, age of the mother and other parameters; if the test results in the first trimester indicate a risk group for fetal chromosomal abnormalities, to exclude the diagnosis of chromosomal abnormalities, the patient is required to consult a geneticist (level 2).

Please note: a well-conducted combined prenatal screening of the 1st trimester makes it unnecessary to conduct biochemical screening of the 2nd trimester. Recently, thanks to the development and application of modern, automated, high-speed, high-precision and concordant methods of biochemical screening I (for example, immunochemiluminescent), as well as due to the high level of ultrasound screening for assessing the risk of congenital malformations and chromosomal pathology in the fetus, clinics for prenatal diagnosis of one visit have appeared - onestop clinics for assessment of risk (OSCAR). Screening for Down's disease and most malformations is carried out by a combined examination, including taking the patient's blood with the determination of biochemical markers from serum samples, ultrasound, followed by counseling at a single visit to the clinic at 12 weeks of gestation. The detectability of trisomy for 21 pairs according to the OSCAR system reaches 90% and has 5% false positive conclusions. Prenatal screening is also practiced in the world using dried blood samples of pregnant women, which are transported to centralized biochemical laboratories for the determination of marker proteins.

STAGE SECOND (LEVEL 1) prenatal screening is carried out in the period of 16 - 24 weeks of pregnancy and includes:

triple (or quarter) biochemical test (the optimal period is 16 - 18 weeks of pregnancy):

Triple biochemical test (“triple Barth test”): blood sampling from pregnant women for serum markers of congenital pathology in the fetus, namely AFP, hCG (alpha-fetoprotein, human chorionic gonadotropin) and free (unconjugated) estriol; according to these indicators, the following risks are calculated: Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), neural tube defects (non-closure of the spinal canal (spina bifida), anencephaly, and other malformations;

Quadruple biochemical test (quadro-test) is the most common and generally accepted today for prenatal screening of the above syndromes (chromosomal abnormalities) with the inclusion of inhibin A (i.e. AFP + hCG + free estriol + inhibin A); an increase in inhibin A levels is associated with an increased risk of Down syndrome in an unborn child; also high inhibin A occurs with other chromosomal abnormalities in the fetus (and nevertheless, many cases have been described when the level of inhibin A during pregnancy was increased several times, but the rest of the tests were normal, and the child was eventually born healthy) .

to calculate the risks based on the results of the combined screening of the second trimester, it is necessary to provide data from the ultrasound examination of the fetus, performed in the first trimester, with the obligatory measurement of CTE.

It should be noted that based on the results of prenatal screening of the I-II trimester of pregnancy, a combined first screening of the I-II trimester of pregnancy (integral test) can be carried out, including: (data from ultrasound of the I trimester and biochemical tests of the I-II trimesters) + computer data processing using a programs; an integral test (two-stage prenatal - the most effective - screening for Down syndrome and Edwards syndrome) is carried out according to the following algorithm (in two stages):

the second stage - is carried out optimally in the period of 16 - 18 weeks of pregnancy (but it is possible to make an analysis up to 22 weeks of pregnancy) AFP, free estriol, inhibin A, hCG in the blood serum are determined.

The advantages of the integral test are that it is a modern alternative to separate double and triple (quarter) tests - the program begins in the first and ends in the second trimester. Of all the options, the integral test has the maximum diagnostic value.

THIRD STAGE (LEVEL 1) prenatal screening is carried out in the period of 32 - 34 weeks of pregnancy and includes:

screening ultrasound examination of pregnant women at 32 - 34 weeks of pregnancy in order to detect congenital malformations in the fetus with late manifestations and to assess the state of fetal development; the doctor establishes the presentation of the child - pelvic or head, makes sure that there is no entanglement with the umbilical cord; this session of ultrasound diagnostics makes it possible to calculate malformations, the signs of which appear only in the third trimester of pregnancy; the last planned ultrasound for parents is no less interesting than the first, as it allows you to see the face of the future baby on the monitor, this is almost a newborn baby; expert-class equipment broadcasts the face of the unborn child in a three-dimensional image, if desired, parents can film this joyful moment on video; as a rule, the third ultrasound is combined with dopplerometry, in the course of this study, the blood flow in the vessels of the embryo, uterus and umbilical cord is studied.

AT LEVEL 2 Examination of pregnant women is carried out in a medical genetic consultation and includes measures for diagnosing specific forms of fetal damage, assessing the severity of the disease and prognosticating the child’s health, as well as resolving issues of termination of pregnancy in cases of a severe disease in the fetus that cannot be treated. Pregnant women of the risk group for congenital malformations and chromosomal pathology in the fetus from health care institutions that monitor pregnant women are sent to medical genetic counseling.

Level 2 activities include:

The following WHO-approved standard indications for referral for invasive prenatal diagnosis (chorionic villus aspiration, placentocentesis, cordocentesis) are available:

Thus, the achievement of reliable and effective prenatal screening is possible only if there is a developed strategy with a system of measures and a clear algorithm of actions, using standard high-tech methods, with the work of highly qualified specialists (involved in prenatal screening), provided that pregnant women with a high degree of motivation for examination are referred in a timely manner and with their full informed consent at all stages of observation.

Doctors recommend conducting the complex of studies under consideration for pregnant women in order to identify abnormalities in the development of the fetus. The patient can refuse such a procedure - it is not mandatory.

Many complain that the process of waiting for results provokes stress, and this negatively affects the bearing of the baby. On the other hand, with information about the presence of any abnormalities in the development of the fetus, a woman has a choice: to terminate the pregnancy, or to raise an unhealthy child in the future.

How is perinatal screening performed?

This set of studies includes ultrasound and carried out in special laboratories.

Referral for perinatal screening issues gynecologist .

If errors are identified in the results obtained, the patient is sent to medical genetic center .

There will be no problems with finding such an institution: it is in every region. The patient can apply to this center on her own, without a referral from the doctor.

This examination during pregnancy is carried out three times:

Initially, an ultrasound is performed, on which the gestational age is accurately determined. This can be done by measuring the coccyx-parietal zone.

When confirming the terms, the doctor prescribes a biochemical screening, the main purpose of which is a dynamic study of the hormone that is produced by the chorion cells (hCG).

Screening at this stage makes it possible to confirm / refute the presence of Down syndrome, Edwards syndrome, and other severe pathologies in the fetus.

The testing in question involves an ultrasound scan, a biochemical blood test for hCG, alpha-fetoprotein, free estriol.

Deciphers the results geneticist . Only the indicated specialist is able to make an adequate “verdict”, taking into account possible errors (toxicosis, non-compliance with the rules for passing the analysis, low weight, etc.).

The presence of abnormalities during the 1st and 2nd screening may indicate the presence of abnormalities in the fetus.

For a more detailed diagnosis, the patient must undergo consultation with a geneticist . The specified doctor prescribes additional diagnostics.

3. From 32 to 34 weeks

The main goal of complex testing at this stage is to study the state of amniotic fluid, the placenta, and the location of the fetus.

In addition to ultrasound, sometimes dopplerometry, cardiotocography can be prescribed. In the course of these diagnostic methods, the quality of blood flow in the vessels of the uterus and umbilical cord is studied.

Main types of perinatal screening

There are several types of pregnancy testing.

Not all of them are mandatory: some of them are assigned to certain groups of patients who, against the background of certain pathologies or negative phenomena, can give birth to an unhealthy child.

Molecular

It is indicative in cases where the future father / mother has patients with a diagnosis of cystic fibrosis, Duchenne modystrophy, hemophilia A and B and some other pathologies in the family.

If the patient wishes, a check for these diseases can be made before pregnancy, or during; in the presence of symptoms - or in the asymptomatic course of pregnancy.

The material for research is venous blood.

Immunological

During this type of screening, blood is taken from a pregnant woman from a vein in order to determine the blood type, Rh factor, as well as TORCH infections (rubella, cytomegalovirus, chicken pox, toxoplasmosis, herpes).

cytogenetic

The type of study under consideration is carried out by a geneticist without the use of any equipment.

During the conversation with the patient, the doctor finds out whether she, her husband or their close relatives have hereditary diseases. The presence of pathologies is the reason for a more detailed diagnosis.

Ultrasonic

It is carried out several times during the gestation of the fetus.

During an ultrasound examination in the first trimester of pregnancy, the doctor pays attention to the following points:

Parameters of the coccyx-parietal zone.
The activity of the heart muscle in the fetus.
The presence of gross defects in the development of the fetus, chromosomal abnormalities.
The quality of attachment of the fetal egg to the uterus.

The results obtained and the age of the expectant mother make it possible to calculate the risk of developing Down's disease.

In the second and third trimester of pregnancy, the specialist checks:

Condition of amniotic fluid, placenta.
This is how the fetus develops.
Whether there are chromosomal abnormalities.

Identification of certain malformations in development after 32 weeks of pregnancy enables the relevant specialists to develop tactics for the surgical treatment of the baby after birth.

Biochemical

The specified type of testing is relevant in the following cases:

The age of the future mother exceeds 35 years.
Spouses or their close relatives have hereditary ailments.
The use of x-rays in the early stages of pregnancy.
Previously, there was a miscarriage, primary infertility or stillbirth.
The use of medications that are toxic to the fetus (this applies to the first trimester of pregnancy).
In the early stages of gestation, there was a negative impact from the environment (radiation, vaporous poisons, etc.)
The parents of the unborn child are connected by blood ties.

Blood components taken from a pregnant woman may indicate various phenomena:

increases with ectopic pregnancy, if there is a threat of miscarriage, with fetal fading (in the second half of pregnancy). This indicator will also be increased if the patient is diagnosed with diabetes mellitus, or the child is born with Down syndrome.
A decrease in the level of the PAPP-A protein can be a harbinger of an early miscarriage, fetal death, and chromosomal diseases.
Alpha protein in the blood of a pregnant woman rises against the background of errors in the structure of the internal organs of the fetus, with the development of Down syndrome, Edwards.
A decrease in estriol is a consequence of multiple pregnancy, or if the expectant mother has problems with the functioning of the kidneys / liver. Elevated estriol often indicates a threat of termination of pregnancy.

Perinatal screening is a special complex that is recommended for almost all pregnant women at an early stage. This study is carried out to completely exclude possible fetal anomalies that have arisen due to a chromosomal or gene disorder. These birth defects are often untreatable, which is why early ultrasound treatment is so important. The term "screening" in translation means "sifting".

Screening of newborns for hereditary diseases consists of a triple ultrasound examination and a biochemical blood test. There is no need to be afraid of this procedure, it is completely safe for both the mother and the baby.

Doctors recommend perinatal screening in the first trimester, between 10 and 14 weeks, with the optimal period being from 11 to 13 weeks. The study helps to assess the course of pregnancy according to all the required parameters, the fact of the development of multiple pregnancy. However, the main purpose of ultrasound at this time is to determine the thickness of the collar space of the embryo. In itself, the collar space is a zone of fluid accumulation between the soft tissues of the neck. In the event that the obtained value exceeds the permissible norm, the risk of a genetic abnormality in the development of the fetus is likely.

Only by ultrasound it is impossible to draw a conclusion, a whole range of studies is needed, which are included in the perinatal. Only on the basis of a comprehensive study can conclusions be drawn. In general, a biochemical blood test is also called a “double test”, and it is done for a period of 10-13 weeks. During this study, the level of two placental proteins is examined in the woman's blood.

Based on the results of an ultrasound examination, the calculation of a possible genetic risk, and after obtaining data on the protein level, a risk calculation is carried out using a computer program. Such a specialized program allows you to take into account even such factors as a woman's ethnicity, her age, weight. Also, the calculation takes into account the fact of the presence of hereditary diseases in the family and family, the presence of various chronic diseases. After a comprehensive study, the doctor examines the results and is able to attribute pregnancy to a risk group, such as Edwards syndrome and However, even in this case, such a threat is not a diagnosis, but only suggests a possibility. Only an experienced geneticist can accurately determine, who will prescribe a further examination. This procedure is more complicated, an instrument is inserted into the abdominal wall and a part of the chorion is taken. Such a biopsy is more dangerous because it can lead to some complications.

Perinatal screening should be done exactly at this time, since the accuracy of the result is maximum during this period. In the case when the tests are given too late or too early, the accuracy of the result is reduced several times. If a woman has an irregular menstrual cycle, then thanks to an ultrasound examination, the gestational age can be accurately determined. The next such examination must be completed at a later date, approximately 16-18 weeks.

The first perinatal screening is a very exciting and touching event. A woman will meet her baby for the first time, see his arms, legs, face. From an ordinary medical examination, it turns into a real holiday for mom and dad of the baby. The main thing to remember is that any deviations from the norm are simply referred to as a risk group, and not a diagnosis. In this case, you do not need to be upset, it is better to just conduct an additional examination.

When pregnancy occurs, expectant mothers begin to be overcome by fear: is everything all right with the baby? Fortunately, modern diagnostic methods allow early detection of fetal developmental disorders. There is such a thing as prenatal screening. This is nothing more than a set of instrumental and laboratory research methods designed to identify the risk of developing congenital pathologies.

Table of contents:

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There is a certain list of laboratory tests that all pregnant women should undergo. Prenatal screening is not mandatory for everyone, but only for those women who are at particular risk for congenital anomalies.

So, screening should be done in such cases:

Pregnant over 35 years old;
If the family already has children with chromosomal abnormalities;
Obstetric history of two or more miscarriages;
If in the first trimester a woman took medications prohibited during pregnancy;
The child's parents are close relatives;
If the parent underwent a course of radiation before conceiving a child;
The threat of abortion.

Screening studies are carried out in each trimester. Conducting research in the first and second trimesters is of the greatest importance.

1st trimester screening

The first screening is a screening done in the first trimester. The most acceptable timing is 10-13 weeks of pregnancy. The first screening allows you to identify congenital malformations at an early stage.

Screening in the first trimester includes:

fetal ultrasound;
Biochemical study of blood.

Ultrasound of the fetus in the first trimester

Allows you to determine the location of organs, the length of the body of the fetus, head circumference, measure the thickness of the neck fold, coccygeal-parietal size.

The coccygeal-parietal size (KTR) is the length measured from the coccyx to the parietal region of the skull. If, during an ultrasound scan, the specialist determined that the CTE is less than expected, this may indicate:

Incorrectly calculated gestational age;
Violation of the development of the fetus as a result of hormonal, infectious diseases of the mother;
The presence of a genetic pathology;
Incorrect position of the fetus, which does not allow to fully measure the distance.

Measurement of such an indicator as biparietal size (BDP) allows you to study the formation of the brain. Biparietal size is the distance from one temple to another. A decrease in BDP indicates an underdevelopment of the brain, and an increase indicates dropsy of the brain.

The probability of chromosomal abnormalities allows you to determine the study of the thickness of the collar space (NTP). An increase in TPV may signal Down syndrome, Edwards, Turner, Patau.

No less significant in the ultrasound examination of the fetus is the determination of the length of the nasal bone. In the presence of a chromosomal pathology, the formation of the nasal bone is delayed. Accordingly, its absence or small size may signal a chromosomal pathology.

Biochemical blood test

For biochemical research, blood is taken from a vein of a pregnant woman. Blood sampling is carried out on an empty stomach in the morning. Of greatest interest is the determination of the levels of human chorionic gonadotropin (hCG), as well as plasma protein (PAPP-A) in the blood of a pregnant woman.

HCG is synthesized by chorion cells. Hormone levels correlate with gestational age.

Chorionic gonadotropin has two fractions: alpha and beta. For the diagnosis of congenital pathology, the determination of the level of beta-hCG is of the greatest importance. A decrease in hCG below the normal level is observed with ectopic pregnancy, placental pathology, Edwards syndrome. And an increase in hCG may indicate:

Multiple pregnancy;
Genetic diseases of the fetus.

Determination of plasma protein PAPP-A produced from the 8th week of pregnancy. It is noteworthy that the definition of this indicator after the 14th week is no longer so reliable.

A decrease in PAPP-A in comparison with normal values characteristic of a certain period of pregnancy indicates:

Chromosomal abnormalities of the fetus;
The threat of miscarriage.

It should be noted that an increase in plasma hormone may also indicate the presence of fetal developmental disorders.

Screening in the second trimester, first of all, is carried out to confirm or refute the results of the first screening, as well as when indicated. The second screening is recommended to take place at the 16-20th week of pregnancy.

Pregnant women carry out such studies:

Biochemical study of the fetus (hCG, AFP, estriol).

Ultrasound of the fetus in the second trimester

The need for ultrasound in the second trimester is dictated by the fact that important functional systems have already formed during this period, the study of which will allow us to assess the development of the child. Ultrasound helps to study:

Proper formation of the spine, limbs;
The length of the nasal bone;
Dimensions of brain structures;
Functioning of internal organs;
The main parameters of the child;
The size and structure of the placenta;
The size of the cervix;
Amniotic fluid level;
fetal heart rate;
The length of the umbilical cord;
The condition of the appendages of a pregnant woman.

Examination of the placenta allows the doctor to determine its location. Normally, the placenta is located on the back wall of the uterus, approximately 6-8 cm above the internal os. If it is located at the bottom of the uterus and closes the internal pharynx, this is a deviation from the norm.

The location of the umbilical cord plays an equally important role; normally, it is attached to the central region of the placenta. There are other atypical options for placing the umbilical cord: marginal, sheath, split. Such anomalies can lead to difficulties during childbirth, in particular, to the freezing of the fetus.

The umbilical cord has three vessels: two arteries and a vein. If at least one artery is missing, this can lead to a violation of the formation and development of the internal organs of the child.

During an ultrasound examination, the doctor can calculate the level of amniotic fluid. What can this indicator say? With oligohydramnios, there is a risk of forming a defect in the limbs, spine, and organs of the nervous system.

Biochemical blood test

Estriol is a hormone responsible for the formation of the placenta. A high level of this hormone can be determined with multiple pregnancies, as well as with a large fetal weight. And a low level can inform about fetoplacental insufficiency, the threat of miscarriage, hypoplasia.

Alpha-fetoprotein (AFP) is a protein synthesized by the fetal liver. The substance enters the mother's body through the placenta, making it possible to determine its concentration by examining the venous blood of the pregnant woman.

A low ACE level is observed when:

Down syndrome;
Edwards syndrome;
Vesical skid;
Fetal death.

A high concentration of alpha-fetoprotein may indicate:

Hernia in the navel;
Abnormal formation of the neural tube of the fetus;
Abnormal formation of the esophagus or duodenum;
Meckel syndrome.

First of all, it is worth noting that screening is a complex study. And this means that if one of the results is unsatisfactory, and the rest are normal, this does not indicate the presence of pathology. Moreover, even if the results in the aggregate are unsatisfactory, this does not mean that the child is 100% likely to be born sick. Screening allows you to assess only the likelihood of developing a pathology in a particular child.

If the doctor deems it necessary, he will refer the woman to a geneticist. With a high risk of congenital pathologies, the pregnant woman is sent for amniocentesis or a chorionic villus biopsy. Amniocentesis allows a specialist to detect the presence of congenital and hereditary diseases by examining the amniotic fluid.

A chorionic villus biopsy also reveals chromosomal pathologies and genetic diseases.

Remember: the doctor makes a conclusion about the risk of having a baby with a pathology based on the results of all screening studies. Having received an unsatisfactory result in your hands, in no case should you panic. The doctor will recommend to undergo additional studies, the results of which can refute all worries about the child's health.

Grigorova Valeria, medical commentator

The Center for Immunology and Reproduction has been successfully working for many years prenatal screening program. Our specialists are invited to give lectures at specialized conferences and in other clinics. Our laboratory receives consistently good marks in the quality control system. Specially trained specialists carry out risk assessment.

What is prenatal diagnosis?

The word "prenatal" means "prenatal". Therefore, the term "prenatal diagnosis" means any research that allows you to clarify the condition of the fetus. Since human life begins from the moment of conception, various health problems can occur not only after birth, but also before birth. Problems can be different:

fairly harmless, with which the fetus can handle itself,
more serious, when timely medical care will save the health and life of the intrauterine patient,
severe enough that modern medicine can not cope.

To determine the state of health of the fetus, prenatal diagnostic methods are used, which include ultrasound, cardiotocography, various biochemical studies, etc. All these methods have different capabilities and limitations. Some methods are quite safe, such as ultrasound. Some carry some risk to the fetus, such as amniocentesis (amniotic fluid sampling) or chorionic villus sampling.

It is clear that methods of prenatal diagnosis, associated with the risk of pregnancy complications, should be used only when there are strong indications for their use. In order to narrow the circle of patients who need invasive (i.e., those associated with intervention in the body) methods of prenatal diagnosis as much as possible, a selection is used risk groups the development of certain problems in the fetus.

What are risk groups?

Risk groups are such groups of patients among whom the probability of detecting a particular pathology of pregnancy is higher than in the entire population (among all women in a given region). There are risk groups for the development of miscarriage, gestosis (late toxicosis), various complications in childbirth, etc. If a woman, as a result of an examination, is at risk for a particular pathology, this does not mean that this pathology will necessarily develop. This only means that in this patient one or another type of pathology may occur with a greater probability than in other women. Thus, the risk group is not identical to the diagnosis. A woman may be at risk, but there may not be any problems during pregnancy. And vice versa, a woman may not be at risk, but she may have a problem. Diagnosis means that this or that pathological condition has already been detected in this patient.

Why are risk groups needed?

Knowing that the patient is in a particular risk group helps the doctor to plan the tactics of pregnancy and childbirth correctly. Identification of risk groups helps protect patients who are not at risk from unnecessary medical interventions, and vice versa, allows you to justify the appointment of certain procedures or studies for patients at risk.

What is screening?

The word screening means "sifting". In medicine, screening is understood as the conduct of simple and safe studies of large groups of the population in order to identify risk groups for the development of a particular pathology. Prenatal screening refers to studies conducted on pregnant women to identify risk groups for pregnancy complications. A special case of prenatal screening is screening to identify risk groups for the development of congenital malformations in the fetus. Screening does not allow to identify all women who may have a particular problem, but it makes it possible to identify a relatively small group of patients, within which most of the people with this type of pathology will be concentrated.

Why screening for fetal malformations is needed?

Some types of congenital malformations in the fetus are quite common, for example, Down's syndrome (trisomy on the 21st pair of chromosomes or trisomy 21) - in one case in 600 - 800 newborns. This disease, as well as some other congenital diseases, occurs at the moment of conception or at the earliest stages of embryonic development, and with the help of invasive methods of prenatal diagnosis (chorionic villus biopsy and amniocentesis) can be diagnosed at a fairly early stage of pregnancy. However, such methods are associated with a risk of a number of pregnancy complications: miscarriage, the development of a conflict according to the Rh factor and blood type, infection of the fetus, the development of hearing loss in a child, etc. In particular, the risk of miscarriage after such studies is 1:200. Therefore, these studies should be prescribed only to women in high risk groups. Risk groups include women over 35 and especially over 40, as well as patients with the birth of children with malformations in the past. However, children with Down syndrome can also be born to very young women. Screening methods - completely safe studies conducted at certain stages of pregnancy - make it possible with a very high degree of probability to identify groups of women at risk of Down's syndrome who may be indicated for a chorionic villus biopsy or amniocentesis. Women who are not at risk do not need additional invasive studies. Finding an increased risk of fetal malformations through screening methods is not a diagnosis. The diagnosis can be made or rejected with additional tests.

What types of birth defects are screened for?

Down syndrome (trisomy of the twenty-first pair of chromosomes)
Edwards syndrome (trisomy eighteenth pair)
Neural tube defects (spina bifida and anencephaly)
Smith-Lemli-Opitz syndrome
Corneli de Lange syndrome

What types of tests are performed as part of the screening for the risk of fetal malformations?

By types of research allocate:

Biochemical screening: blood test for various indicators
Ultrasound Screening: detection of signs of developmental anomalies using ultrasound.
Combined screening: a combination of biochemical and ultrasound screenings.

The general trend in the development of prenatal screening is the desire to obtain reliable information about the risk of developing certain disorders as early as possible in pregnancy. It turned out that combined screening at the end of the first trimester of pregnancy (terms of 10-13 weeks) makes it possible to approach the effectiveness of classical biochemical screening of the second trimester of pregnancy.

Ultrasound screening, used for mathematical processing of the risks of fetal anomalies, is carried out only 1 time: at the end of the first trimester of pregnancy.

Concerning biochemical screening, then the set of indicators will be different at different stages of pregnancy. During pregnancy 10-13 weeks The following parameters are checked:

free β-subunit of human chorionic hormone (free β-hCG)
PAPP-A (pregnancy associated plasma protein A), pregnancy-associated plasma protein A

The calculation of the risk of measuring fetal anomalies, based on the measurement of these indicators, is called double biochemical test of the first trimester of pregnancy.

Using a double test in the first trimester, the risk of detection in the fetus is calculated Down syndrome (T21) And Edwards syndrome (T18), trisomy on chromosome 13 (Patau syndrome), triploidy of maternal origin, Shereshevsky-Turner syndrome without dropsy. The risk of neural tube defects cannot be calculated using the dual test, since the key indicator for determining this risk is α-fetoprotein, which begins to be determined only from the second trimester of pregnancy.

Special computer programs make it possible to calculate the combined risk of fetal anomalies, taking into account the biochemical parameters determined in the first trimester double test and the results of an ultrasound scan taken at 10-13 weeks of gestation. Such a test is called combined with TVP double test of the first trimester of pregnancy or triple test first trimester of pregnancy. The results of risk calculations obtained using a combined double test are much more accurate than risk calculations based only on biochemical parameters or only on the basis of ultrasound.

If the results of the test in the first trimester indicate a risk group for chromosomal abnormalities of the fetus, the patient may be performed to exclude the diagnosis of chromosomal abnormalities chorionic villus biopsy.

During pregnancy 14 - 20 weeks by last menstrual period recommended terms: 16-18 weeks) the following biochemical indicators are determined:

α-fetoprotein (AFP)
Inhibin A

Based on these indicators, the following risks are calculated:

Down syndrome (trisomy 21)
Edwards syndrome (trisomy 18)
neural tube defects (non-closure of the spinal canal (spina bifida) and anencephaly).
Risk of trisomy 13 (Patau syndrome)
Triploid maternal origin
Shereshevsky-Turner syndrome without dropsy
Smith-Lemli-Opitz syndrome
Corneli de Lange syndrome

Such a test is called Quadruple test in the second trimester of pregnancy or quadruple biochemical screening in the second trimester of pregnancy. A truncated version of the test is the so-called triple or double tests of the second trimester, which includes 2 or indicators: hCG or free hCG β-subunit, AFP, free estriol. It is clear that the accuracy of the double or double II trimester test is lower than the accuracy of the quadruple II trimester test.

Another option for biochemical prenatal screening is biochemical screening for the risk of only neural tube defects in the second trimester of pregnancy. In this case, only one biochemical marker is determined: α-fetoprotein

When is the second trimester screening done in pregnancy?

At 14 - 20 weeks of pregnancy. The optimal period is 16 - 18 weeks of pregnancy.

What is a 2nd trimester quad test?

The main option for biochemical screening of the second trimester in the CIR is the so-called quadruple or quadruple test, when the determination of inhibin A is added to the determination of the three above indicators.

Ultrasound screening in the first trimester of pregnancy.

In the first trimester of pregnancy, the main dimension used in calculating risks is the width of the cervical translucency (English "nuchal translucency" (NT) , French "clarté nuchale"). In Russian medical usage, this term is often translated as "collar space" (TVP) or "neck fold". Cervical transparency, collar space and cervical fold are full synonyms that can be found in various medical texts and mean the same thing.

Cervical transparency - definition

Cervical transparency is what an accumulation of subcutaneous fluid on the back of the fetal neck looks like on ultrasound during the first trimester of pregnancy.
The term "cervical transparency" is used regardless of whether it has septa or whether it is limited to the cervical region or surrounds the entire fetus.
The frequency of chromosomal and other anomalies is primarily related to the width of the transparency, and not how it looks in general.
During the second trimester, the transparency usually resolves, but in some cases it can turn into either cervical edema or cystic hygromas with or without generalized edema.

Measurement of cervical transparency

Terms of pregnancy and coccyx-parietal size

The optimal gestational age for measuring NB is 11 weeks to 13 weeks 6 days. The minimum size of the KTP is 45 mm, the maximum is 84 mm.

There are two reasons for choosing 11 weeks as the earliest time to measure NB:

Screening requires the ability to perform a chorionic villus biopsy before the time when this study may be complicated by amputation of the fetal limbs.
On the other hand, many gross fetal defects can only be detected after 11 weeks of pregnancy.

The diagnosis of omphalocele is possible only after 12 weeks.
Diagnosis of anencephaly is possible only after 11 weeks of pregnancy, since only from this period do ultrasound signs of ossification of the fetal skull appear.
Assessment of the four-chambered heart and large vessels is possible only after 10 weeks of pregnancy.
The bladder is visualized in 50% of healthy fetuses at 10 weeks, in 80% at 11 weeks, and in all fetuses at 12 weeks.

Image and measurement

To measure FN, the ultrasonic machine must have a high resolution with video loop function and calibrators that can measure the size to tenths of a millimeter. SP can be measured with an abdominal probe in 95% of cases, in cases where this cannot be done, a vaginal probe should be used.

Only the head and upper part of the thorax of the fetus should be included in the image when measuring the CW. The magnification should be maximum, so that a small shift of the markers gives a change in measurement of no more than 0.1 mm. When zooming in on an image, either before or after fixing the image, it is important to reduce the gain. This avoids a measurement error when the marker falls into a blurred area and thus the size of the NR will be underestimated.

A good sagittal section should be obtained, of the same quality as when measuring CTE. The measurement should be made in the neutral position of the fetal head: extension of the head can increase the value of TBP by 0.6 mm, flexion of the head can decrease the value by 0.4 mm.

It is important not to confuse the skin of the fetus and the amnion, since at this stage of pregnancy both formations look like thin membranes. If in doubt, you should wait for the moment when the fetus makes a movement and moves away from the amnion. An alternative way is to ask the pregnant woman to cough or lightly tap on the pregnant woman's abdominal wall.

The largest perpendicular distance between the internal contours of the cervical transparency is measured (see figure below). Measurements are taken three times, the largest value of the size is used for the calculation. In 5-10% of cases, the umbilical cord is found wrapped around the fetal neck, which can greatly complicate measurement. In such cases, 2 measurements are used: above and below the cord entanglement, the average of these two measurements is used to calculate the risks.

Standards for ultrasound scanning at the end of the first trimester of pregnancy are being developed by the England-based Fetal Medicine Foundation (FMF). In the CIR group of companies, ultrasound is performed according to the FMF protocol.

Additional Ultrasound Signs of Down Syndrome Risk

Recently, in addition to the measurement of SP for the diagnosis of Down syndrome at the end of the first trimester of pregnancy, the following ultrasound signs are used:

Definition of the nasal bone. At the end of the first trimester, the nasal bone not defined using ultrasound in 60-70% of fetuses with Down syndrome and only in 2% of healthy fetuses.
Assessment of blood flow in the Arantzian (venous) duct. Abnormalities in the waveform of blood flow in the duct of Arantia are found in 80% of fetuses with Down's syndrome and only in 5% of chromosomally normal fetuses.
Reducing the size of the maxillary bone
Bladder enlargement (“megacystitis”)
Moderate tachycardia in the fetus

The shape of the blood flow in the duct of Arantia with dopplerometry. Top: normal; bottom: with trisomy 21.

Not only Down syndrome!

During the ultrasound at the end of the first trimester, the assessment of the fetal contour delivers to reveal the following fetal anomalies:

Exencephaly - anencephaly
Cystic hygroma (swelling at the level of the neck and back of the fetus), more than half of the cases due to chromosomal abnormalities
Omphalocele and gastroschisis. The diagnosis of omphalocele can only be made after 12 weeks of pregnancy, since before this period the physiological umbilical hernia, which is quite often detected, has no clinical significance.
The only umbilical artery (in a large percentage of cases it is combined with chromosomal abnormalities in the fetus)

How are risks calculated?

Special software is used to calculate risks. Simply determining the level of indicators in the blood is not enough to decide whether the risk of developmental anomalies is increased or not. The software must be certified for use with prenatal screening. At the first stage of computer calculation, the figures of indicators obtained during laboratory diagnostics are converted into the so-called MoM (multiple of median, a multiple of the median), characterizing the degree of deviation of one or another indicator from the median. At the next stage of the calculation, the MoM is adjusted for various factors (a woman's body weight, race, the presence of certain diseases, smoking, multiple pregnancy, etc.). The result is the so-called adjusted MoM. In the third step of the calculation, the adjusted MoMs are used to calculate the risks. The software is specially configured for the methods used in the laboratory for determining indicators and reagents. It is unacceptable to calculate risks using analyzes made in another laboratory. The most accurate calculation of the risks of fetal anomalies is when using data from an ultrasound scan performed at 10-13 weeks of gestation.

What is MOM?

MoM is the English abbreviation for the term “multiple of median”, which means “multiple of the median”. This is a coefficient showing the degree of deviation of the value of one or another indicator of prenatal screening from the average value for the gestational age (median). MoM is calculated using the following formula:

MoM = [Mean value in patient's serum] / [Median value for gestational age]

Because the measure value and the median share the same units, the MoM value has no units. If the value of MoM in a patient is close to one, then the value of the indicator is close to the average in the population; if it is above one, it is above the average in the population; if it is below one, it is below the average in the population. With congenital malformations of the fetus, there may be statistically significant deviations of MoM markers. However, in its pure form, MoMs are almost never used in calculating the risk of fetal anomalies. The fact is that in the presence of a number of factors, the average values of MoM deviate from the average in the population. Such factors include the patient's body weight, smoking, race, pregnancy as a result of IVF, etc. Therefore, after obtaining the MoM values, the risk calculation program makes an adjustment for all these factors, resulting in the so-called “adjusted MoM value”, which used in risk calculation formulas. Therefore, in the conclusion forms based on the results of the analysis, next to the absolute values of the indicators, the adjusted MoM values for each indicator are indicated.

Typical MoM profiles in pregnancy pathology

With various fetal anomalies, MoM values are combined deviated from the norm. Such combinations of MoM deviations are called MoM profiles for a particular pathology. The tables below show typical MoM profiles at different gestational ages.

Typical MoM Profiles - First Trimester

Typical MoM Profiles - Second Trimester

Indications for 1st and 2nd trimester prenatal screening for risk of fetal anomalies

Prenatal screening is now recommended for all pregnant women. The order of the Ministry of Health of the Russian Federation of 2000 obliges antenatal clinics to conduct biochemical prenatal screening for all pregnant patients in the second trimester of pregnancy for two indicators (AFP and hCG).

Order No. 457 of December 28, 2000 “On improving prenatal diagnosis in the prevention of hereditary and congenital diseases in children”:

“At 16-20 weeks, take blood from all pregnant women to conduct studies of at least two serum markers (AFP, hCG)”

The importance of monitoring congenital diseases on an ongoing basis in Moscow is also discussed in the Moscow government's decree on the establishment of the city's Children's Health Program for 2003-2005.

"It is advisable to start genetic monitoring of congenital malformations of newborns, prenatal screening for Down's disease and neural tube defects in Moscow"

On the other hand, prenatal screening should be purely voluntary. In most Western countries, it is the physician's responsibility to inform the patient about the possibility of such studies and about the goals, possibilities and limitations of prenatal screening. The patient herself decides whether to do her tests or not. The same point of view is shared by the CIR group of companies. The main problem is that there is no cure for the detected anomalies. If the presence of anomalies is confirmed, the couple is faced with a choice: terminate the pregnancy or keep it. It's not an easy choice.

What is Edwards Syndrome?

This is a condition caused by the presence of an extra 18th chromosome in the karyotype (trisomy 18). The syndrome is characterized by gross physical anomalies and mental retardation. This is a lethal condition: 50% of sick children die in the first 2 months of life, 95% - during the first year of life. Girls are affected 3-4 times more often than boys. The frequency in the population ranges from 1 case per 6,000 births to 1 case per 10,000 births (about 10 times less than Down syndrome).

What is the free β-subunit of hCG?

The molecules of a number of pituitary and placental hormones (thyroid stimulating hormone (TSH), follicle stimulating hormone (FSH), luteinizing hormone (LH) and human chorionic hormone (hCG)) have a similar structure and consist of α and β subunits. The alpha subunits of these hormones are very similar and the main differences between the hormones are in the structure of the β subunits. LH and hCG are very similar not only in the structure of the α-subunits, but also in the structure of the β-subunits. That is why they are hormones with the same action. During pregnancy, LH production by the pituitary gland drops to almost zero, and hCG concentrations are very high. The placenta produces very large amounts of hCG, and although this hormone mainly enters the blood in an assembled form (a dimeric molecule consisting of both subunits), a small amount of free (not bound to the α-subunit) β-hCG subunit also enters the bloodstream. Its concentration in the blood is many times less than the concentration of total hCG, but this indicator can more reliably indicate the risk of problems in the fetus in the early stages of pregnancy. The determination of the free β-subunit of hCG in the blood is also important for the diagnosis of trophoblastic disease (molar mole and chorionepithelioma), some testicular tumors in men, and monitoring the success of in vitro fertilization procedures.

Which indicator: total hCG or free β-hCG subunit - is it preferable to use in the second trimester triple test?

Using free hCG β-subunit determination compared to total hCG determination gives a more accurate estimate of the risk of Down syndrome, however, in the classic statistical calculations of the risk of Edwards syndrome in the population, the determination of the level of total hCG in the mother's blood was used. For the β-subunit of hCG, no such calculations have been made. Therefore, a choice must be made between a more accurate calculation of the risk of Down syndrome (in the case of the β-subunit) and the possibility of calculating the risk of Edwards syndrome (in the case of total hCG). Recall that in the first trimester, only free β-subunit hCG is used to calculate the risk of Edwards syndrome, but not total hCG. Edwards syndrome is characterized by low numbers of all 3 indicators of the triple test, therefore, in such cases, both variants of the triple test (with total hCG and with free β-subunit) can be done.

What is PAPP-A?

Pregnancy-associated plasma protein-A (PAPP-A) was first described in 1974 as a high molecular weight protein fraction in the blood serum of women in late pregnancy. It turned out to be a large zinc-containing metalglycoprotein with a molecular weight of about 800 kDa. During pregnancy, PAPP-A is produced by syncytiotrophoblast (the tissue that is the outer layer of the placenta) and extravillous cytotrophoblast (islands of fetal cells in the thickness of the uterine lining) and enters the mother's bloodstream.

The biological significance of this protein is not fully understood. It has been shown to bind heparin and is an inhibitor of granulocyte elastase (an enzyme induced by inflammation), so it is suggested that PAPP-A modulates the maternal immune response and is one of the factors that ensures the development and survival of the placenta. In addition, it was found that it is a protease that cleaves protein 4 that binds insulin-like growth factor. There are serious reasons to believe that PAPP-A is one of the factors of paracrine regulation not only in the placenta, but also in some other tissues, in particular, in atherosclerotic plaques. It is proposed to use this marker as one of the risk factors for coronary heart disease.

Maternal blood concentrations of PAPP-A steadily increase with increasing gestational age. The greatest increase in this indicator is observed at the end of pregnancy.

Over the past 15 years, PAPP-A has been studied as one of three risk markers for trisomy 21 (Down syndrome) (together with free hCG β-subunit and nuchal thickness). It turned out that the level of this marker at the end of the first trimester of pregnancy (8-14 weeks) is significantly reduced if the fetus has trisomy 21 or trisomy 18 (Edwards syndrome). The uniqueness of this indicator is that its significance as a marker of Down syndrome disappears after 14 weeks of pregnancy. In the second trimester, its levels in maternal blood in the presence of trisomy 21 in the fetus do not differ from those in pregnant women with a healthy fetus. If we consider PAPP-A as an isolated marker of the risk of Down syndrome in the first trimester of pregnancy, its determination at 8-9 weeks would be the most significant. However, the free β-subunit of hCG is a stable marker of the risk of Down syndrome at 10-18 weeks, i.e. later than PAPP-A. Therefore, the optimal time for donating blood for a double test in the first trimester of pregnancy is 10-12 weeks.

The combination of PAPP-A measurement with the determination of the concentration of free β-hCG subunit in the blood and the determination of TVP using ultrasound at the end of the first trimester of pregnancy can identify up to 90% of women at risk of developing Down syndrome in the older age group (after 35 years). The probability of false positive results is about 5%.

In addition to prenatal screening for the risk of Down syndrome and Edwards syndrome, in obstetrics, the definition of PAPP-A is also used for the following types of pathology:

The threat of miscarriage and stopping the development of pregnancy in the short term
Cornelia de Lange syndrome.

Risk Diagnostics arrest of fetal development in early pregnancy was historically the first clinical application for serum PAPP-A, proposed in the early 1980s. Women with low levels of PAPP-A in early pregnancy have been shown to be at risk of subsequent pregnancy arrest and severe forms of late toxicosis. Therefore, it is recommended that this indicator be determined within 7-8 weeks for women with a history of severe pregnancy complications.

Cornelia de Lange syndrome is a rare form of congenital malformation of the fetus, found in 1 case in 40,000 births. The syndrome is characterized by mental and physical retardation, heart and limb defects, and characteristic facial features. It has been shown that in this condition, the levels of PAPP-A in the blood at 20-35 weeks are significantly lower than normal. A study by Aitken's group in 1999 showed that this marker can be used to screen for Cornelia de Lange syndrome in the second trimester of pregnancy, since the levels of the indicator in such pregnant women were on average 5 times lower than normal.

The reagents used to determine PAPP-A and the free β-subunit of hCG are an order of magnitude more expensive than those used for most hormonal parameters, which makes this test more expensive than most reproductive hormones.

What is α-fetoprotein?

It is a fetal glycoprotein produced first in the yolk sac and then in the liver and gastrointestinal tract of the fetus. It is a transport protein in the blood of the fetus that binds a number of different factors (bilirubin, fatty acids, steroid hormones). It is a dual fetus growth regulator. In an adult, AFP does not perform any known functions, although it can increase in the blood in liver diseases (cirrhosis, hepatitis) and in some tumors (hepatocellular carcinoma and germinal carcinoma). In the mother's blood, the level of AFP gradually increases with increasing gestational age and reaches a maximum by 30 weeks. The level of AFP in the mother's blood increases with neural tube defects in the fetus and with multiple pregnancies, and decreases with Down syndrome and Edwards syndrome.

What is free estriol?

Estriol is synthesized in the placenta from 16α-hydroxy-dehydroepiantrosterone sulfate supplied by the fetus. The main source of estriol precursors is the fetal adrenal glands. Estriol is the main estrogenic hormone of pregnancy and ensures the growth of the uterus and the preparation of the mammary glands for lactation.

90% of estriol after 20 weeks of pregnancy is formed from fetal DEA-C. A large output of DEA-C from the adrenal gland of the fetus is associated with low activity of 3β-hydroxysteroid dehydrogenase in the fetus. A protective mechanism that protects the fetus from excess androgenic activity is the rapid conjugation of steroids with sulfate. The fetus produces more than 200 mg of DEA-C per day, 10 times more than the mother. In the maternal liver, estriol is rapidly conjugated with acids, mainly hyaluronic acid, and thus inactivated. The most accurate method for determining the activity of the fetal adrenal glands is to determine the level of free (unconjugated) estriol.

The level of free estriol gradually rises as pregnancy progresses and in the third trimester of pregnancy can be used to diagnose fetal well-being. With a deterioration in the condition of the fetus in the third trimester of pregnancy, a sharp drop in the level of free estriol can be observed. Free estriol levels are often low in Down syndrome and Edwards syndrome. Taking dexamethasone, prednisolone or metipred during pregnancy suppresses the function of the fetal adrenal glands, so the level of free estriol in such patients is often reduced (decrease in the supply of estriol from the fetus). When taking antibiotics, the rate of estriol conjugation in the mother's liver increases and the reabsorption of conjugates from the intestine decreases, so the level of estriol also decreases, but by accelerating its inactivation in the mother's body. For an accurate interpretation of the triple test data, it is very important that the patient provides a complete list of drugs taken or taken during pregnancy with doses and timing of use.

Algorithm for prenatal screening I and II trimester of pregnancy.

1. We calculate the duration of pregnancy, it is better after consulting a doctor or with the help of a consultant.

Screening of the first trimester has its own characteristics. It is carried out in terms of 10 - 13 weeks of pregnancy and is quite strictly limited in time. If you donate blood too early or too late, if you make a mistake in calculating the gestational age at the time of donating blood, the accuracy of the calculation will decrease dramatically. Pregnancy terms in obstetrics are usually calculated on the first day of the last menstruation, although conception occurs on the day of ovulation, that is, with a 28-day cycle - 2 weeks after the first day of menstruation. Therefore, the terms of 10 - 13 weeks on the day of menstruation correspond to 8 - 11 weeks of conception.

To calculate the gestational age, we recommend using the obstetric calendar posted on our website. Difficulties in calculating the timing of pregnancy can be with an irregular menstrual cycle, with pregnancy that occurs shortly after childbirth, with a cycle that deviates more than a week from 28 days. Therefore, it is best to trust professionals, and to calculate the duration of pregnancy, conduct an ultrasound scan and donate blood, consult a doctor.

2. We do an ultrasound.

The next step should be an ultrasound scan at 10-13 weeks of gestation. The data from this study will be used by the risk calculation program in both the first and second trimesters. It is necessary to start the examination with ultrasound, since during the study problems with the development of pregnancy (for example, a stop or lag in development), a multiple pregnancy, the timing of conception will be accurately calculated. The doctor conducting the ultrasound will help the patient calculate the timing of blood donation for biochemical screening. If the ultrasound is done too early in terms of pregnancy, then the doctor may recommend repeating the study after some time.

To calculate the risks, the following data from the ultrasound report will be used: the date of the ultrasound, the coccygeal-parietal size (CTE) and the thickness of the collar space (NTP) (English abbreviations, respectively, CRL and NT), as well as visualization of the nasal bones.

3. We donate blood.

Having the results of the ultrasound and knowing the exact gestational age, you can come for blood donation. Blood sampling for analysis for prenatal screening in the CIR group of companies is carried out daily, including weekends. On weekdays, blood sampling is carried out from 7:45 to 21:00, on weekends and holidays: from 8:45 to 17:00. Blood sampling is carried out 3-4 hours after the last meal.

In terms of pregnancy 14-20 weeks after the last menstruation (recommended terms: 16-18 weeks), the following biochemical parameters are determined:

Total hCG or free β-hCG subunit
α-fetoprotein (AFP)
Free (unconjugated) estriol
Inhibin A

4. We get the result.

Now we need to get the results of the analysis. The turnaround time for the results of prenatal screening analysis in the CIR group of companies is one business day (except for the fourth test). This means that tests taken from Monday to Friday will be ready on the same day, and those taken from Saturday to Sunday on Monday.

Conclusions on the results of the study are issued to the patient in Russian.

Tiblitsa. Explanation of terms and abbreviations

Report date	Date of computer processing of results
Gestational age	Weeks + days
Date of ultrasound	Date of the ultrasound. Usually does not coincide with the date of blood donation.
Fruit	The number of fruits. 1 - singleton pregnancy; 2 - twins; 3 - triplets
ECO	Pregnancy as a result of IVF
KTR	Coccyx-parietal size determined during ultrasound
MoM	Multiple of median, the degree of deviation of the result from the average for a given gestational age
Corr. MoM	Adjusted MoM. MoM value after adjustment for body weight, age, race, number of fetuses, diabetes, smoking, IVF infertility treatment.
NT	The thickness of the collar space (nuchal translucency). Synonym: neck fold. In various versions of reports, either absolute values in mm or the degree of deviation from the median (MoM) can be given
age risk	The average risk for this age group. No factors other than age are taken into account.
Tr. 21	Trisomy 21, Down syndrome
Tr. 18	Trisomy 18, Edwards syndrome
biochemical risk	The risk of fetal anomalies after computer processing of blood test data without taking into account ultrasound data
Combined risk	The risk of fetal anomalies after computer processing of blood test data, taking into account ultrasound data. The most accurate indicator of the degree of risk.
fb-HCG	Free β-hCG subunit
PDM	Date of last menstrual period
AFP	α-fetoprotein
HCG	Total hCG (human chorionic gonadotropin)
uE3	Free estriol (unconjugated estriol)
+NT	The calculation was carried out taking into account ultrasound data
mIU/ml	mIU/ml
ng/ml	ng/ml
IU/ml	IU/ml

Additional Information.

Information for patients: Please note that if you plan to undergo prenatal screening in the CIR group of companies, then the ultrasound data made in other institutions will be taken into account only if there is a special agreement between the CIR group of companies and these institutions.

Information for doctors

Dear Colleagues! In accordance with the Order of the Ministry of Health No. 457 and Decree of the Government of Moscow No. 572, the CIR group of companies provides services to other medical institutions for prenatal screening for the risk of chromosomal abnormalities. You can invite our staff to come to you with a lecture on this program. To refer a patient for screening, the attending physician must complete a special referral. The patient can come to donate blood on her own, but it is also possible to take blood in other institutions with subsequent delivery to our laboratory, including by our courier. If you want to receive the results of double, triple and quadruple tests of the first and second trimesters of pregnancy, combined with ultrasound data, the patient must come to us for an ultrasound scan, or we must sign a special agreement with your institution and include your ultrasound specialists in the program, but only after departure of our expert in functional diagnostics to your institution and familiarization with the quality of the equipment and the qualifications of specialists.