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Prenatal screening for trisomies in the 2nd trimester of pregnancy. Prenatal screening is the most complete information. General information about the study

The study is performed for screening of pregnant women in order to assess the risk of fetal chromosomal abnormalities - trisomy 21 (Down's syndrome), trisomy 18 (Edwards syndrome), neural tube defect (NTD). The quantitative assessment of research results is carried out using the automated PRISCA program.

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:

  1. Human chorionic gonadotropin (hCG, beta-hCG, b-hCG, Human Chorionic gonadotropin, HCG),;
  2. Alpha-fetoprotein (AFP, a-Fetoprotein),;
  3. Free estriol (unconjugated estriol),.

Determination of the concentration of these markers is recommended by the Order of the Ministry of Health of Ukraine No. 417 of 15.07.2011 for biochemical screening of pregnant women in the second trimester of pregnancy in order to assess the risk of fetal chromosomal abnormalities. The study is conducted between 14 and 21 weeks of gestation. The optimal timing of the study is from 16 to 18 weeks of pregnancy.

When referring to the study, a special referral form must be filled out, which indicates the individual data of the pregnant woman. These include age, weight, ultrasound results for accurate calculation of the gestational age with the obligatory indication of the date of ultrasound and the name of the ultrasound doctor (CTE, BPD, number of fetuses, ultrasound gestation, if available, data on the size of the cervical fold - NT nuchal translucency), presence of additional risk factors (smoking, diabetes, IVF), ethnicity. You must also indicate the name of the referring physician.

Attention! This study requires the presence of ultrasound results!

Special indications for the appointment of screening studies to identify the risk of fetal chromosomal abnormalities are:

  • the woman's age is over 35;
  • the presence in the family of a child (or a history of a fetus of an interrupted pregnancy) with genetically confirmed Down's disease, other chromosomal diseases, congenital malformations; hereditary diseases in close relatives;
  • radiation exposure or other harmful effects on one of the spouses before conception.

To complete the study, you must fill out a special referral form.

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.

The results of calculating the risk of fetal chromosomal abnormalities based on screening biochemical studies are statistical probabilistic indicators that are not the basis for a diagnosis, but serve as an indication for further special research methods.

The quantitative assessment of the results obtained during these profile studies will be carried out using the PRISCA automated program (developed by DPC, USA).

When using the PRISCA program, the medians of the reference values ​​are corrected taking into account individual data. To analyze the results, the MoM calculation is used (the ratio of the result obtained in the study to the individually adjusted median of the reference values). The use of an integrated approach increases the value of screening and, according to a number of studies, makes it possible to detect Down syndrome in a fetus in the first trimester of pregnancy in 85 - 90% of cases with 5% of false positive results.

Biomaterial: Blood serum

Term of completion (in the laboratory): 3 w.d. *

Description

The study is performed on Cobas E 8000 equipment from Roche using the Roche – SsdwLab 5.0.14 software.

Optimal timing for second trimester screening: 16-18 weeks. “20th week” means strictly 19 full weeks + 6 days. Samples received the next day are not taken into account by the program.

The study includes: questionnaire data, ultrasound of the second trimester (BPD), laboratory tests (AFP, total hCG), calculation of the risks of chromosomal pathology in the special program Roche – SsdwLab 5.0.14.

Prenatal screening for calculating the individual risk of chromosomal abnormalities in the fetus in the second trimester of pregnancy is used in cases of late registration for pregnancy (after 14 weeks) and in case of a questionable result of prenatal biochemical screening of the first trimester.

Prenatal screening reveals the likelihood of a chromosomal abnormality in the fetus (trisomy on chromosome 21 - Down's syndrome, trisomy on chromosome 18 - Edwards syndrome, trisomy on chromosome 13 - Patau syndrome), as well as neural tube defects.

For the determination of biochemical markers, the CITILAB laboratory has modern high-precision Cobas E 8000 platforms from Roche. This company is one of three that have passed the Fetal Medicine Foundation (FMF, International Fetal Medicine Foundation, UK) and is accredited to conduct prenatal screening tests.

Roche Cobas E 8000 platforms show the best reproducibility of results compared to alternative methods - CV-3%, which even exceeds the FMF requirements (6%).

For computer processing and data acquisition, the certified Roche program - SsdwLab 5.0.14 is used, which allows calculating the risks of the second trimester from the 14th to the 19th week + 6 days, based on ultrasound data and biochemical markers. St. Petersburg, Publishing House "Petropolis", 2007 - 144)

Discounts are not provided for this study (see the Regulation on discounts)

The study is performed on Cobas E 8000 equipment from Roche using the Roche – SsdwLab 5.0.14 software. Optimal timing for screening

Indications for appointment

  • the presence of questionable results of biochemical screening in the first trimester;
  • registration for pregnancy for a period of more than 14 weeks;
  • the age of the pregnant woman is more than 35 years old;
  • the presence in the family of a child or in the history of a fetus of an interrupted pregnancy with a genetically confirmed diagnosis of Down syndrome, other chromosomal abnormalities, congenital malformations;
  • the presence of hereditary diseases in close relatives;
  • if both or one of the spouses before conception were exposed to radiation exposure, harmful effects of physical or chemical factors.

Preparation for research

Important! It is permissible to draw blood and conduct an ultrasound scan with a difference of 3 days!
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 non-carbonated and non-mineral water).
It is permissible to take blood in the afternoon 4 hours after a light meal.
On the eve of the study, it is necessary to exclude increased psychoemotional and physical stress. Do not smoke for 1 hour before the study.

Interpretation of results / Information for specialists

The interpretation of the results is provided by the obstetrician-gynecologist who leads the pregnancy.

The risks of fetal chromosomal pathology are assessed based on the deviation of the results of determining biochemical markers and ultrasound data (thickness of the collar space) from the reference values. However, the reference level of markers (PAPP-A, AFP, b-hCG, hCG, free estriol) may vary in different populations and ethnic groups. In this regard, individual levels of markers in pregnant women are usually assessed using the median of these indicators at different stages of normal pregnancy and the MoM (Multiple of Median) indicator. Median values ​​are derived from a large number of multicenter randomized trials.

The median corresponds to the value of the indicator for a conditionally “average” woman, while 50% of women with the same gestational age have values ​​lower, and the other 50% are higher than the median. The MoM indicator is the ratio of the individual marker value to the median of the corresponding reference series established for a certain population. Therefore, the reference values ​​of serum markers for any gestational age are MoM values ​​from 0.5 to 2.0. It has been established that in Down's syndrome the average AFP level is 0.7 MoM, CG - 2 MoM, estriol 0.75 MoM. In Edwards syndrome, the level of AFP, hCG and estriol is 0.7 MoM. When considering the distribution curves of the values ​​of the main markers, a large area of ​​overlap between norm and pathology is observed, this does not allow using only one marker for screening, a full complex of markers is required.

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* The site indicates the maximum possible term for the study. It reflects the time it takes to complete a study in the laboratory and does not include the time it takes to deliver the biomaterial to the laboratory.
The information provided is for reference only and is not a public offer. For up-to-date information, contact the Contractor's medical center or call-center.

> Prenatal screening for trisomies of the first and second trimesters of pregnancy

This information cannot be used for self-medication!
Consultation with a specialist is imperative!

What is prenatal screening and what is it for?

Prenatal screening is a series of medical procedures aimed at detecting congenital chromosomal abnormalities in the development of the fetus. It is based on the determination of some biochemical markers in the blood of a pregnant woman, the analysis of the results obtained, taking into account the data of ultrasound examination of the fetus. In particular, with the help of screening, it is possible to identify such pathology as trisomy - the presence of an additional chromosome.

For pregnant women, prenatal screening for trisomy is done in the first trimester, the so-called "double test", and in the second trimester, the "triple test".

Who prescribes prenatal screening, where are the tests done?

The referral for these tests is given by an obstetrician-gynecologist or a medical geneticist. Blood, which acts as a biological material, is donated in a biochemical laboratory or in a procedure room of an antenatal clinic. Ultrasound of the fetus is performed by an ultrasound doctor.

Indications for prenatal screening for trisomy

The "double test" is performed between 10 weeks and 13 weeks of gestation. It is used to determine the risk of Down syndrome (trisomy 21 chromosomes), Edwards syndrome (trisomy 18 chromosomes), and NTD (neural tube defect). NTD is a gross disorder in the development of the nervous system, as a result of which a spinal hernia is formed. The "triple test" is carried out at a gestational age of 14 weeks to 22nd.

Tests are prescribed not for all women in a row, but under the following conditions: the woman's age is more than 35 years, a history of severe complications of pregnancy or miscarriage. Congenital anomalies in children from previous pregnancies, the presence of a similar pathology in close relatives, infection, taking mutagenic drugs are the basis for screening for trisomy.

How is screening for trisomy done, preparation for analysis

To calculate the risk of trisomies, pregnant women donate blood to determine the concentration of certain hormones in it. Screening for the first trimester involves determining the concentrations of human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein A. In the second trimester, hCG, alpha-fetoprotein (AFP) and free estriol are determined.

In addition to the study of biochemical markers, an ultrasound examination of the fetus is performed, during which the thickness of the collar zone, the coccyx-parietal size of the fetus, and the biparietal size are assessed.

Normal screening results

The results obtained are entered into a special computer program - PRISCA. In addition to the values ​​of biochemical indicators, ultrasound data, it takes into account the presence of bad habits, the exact duration of pregnancy, the presence of multiple pregnancies.

The program issues a conclusion in the form of a form, which displays all of the above indicators and a conclusion about the likelihood of having a child with pathology. For example, a result of 1: 500 suggests that one in 500 women with similar rates may have a baby with trisomy.

Clinical significance of the study

Patients should be aware that screening for trisomy calculates only the probability of having a child with a pathology, and does not mean that the child will certainly have a pathology. Therefore, at a very high risk, the patient must undergo additional research - amniocentesis, followed by the study of the genetic material of the fetus. Only the results of this study are the basis for the doctor's decision to terminate the pregnancy.

Prenatal or antenatal screening is a special examination of pregnant women, during which the risk of having children with a gross congenital chromosomal abnormality is determined.

"Triple biochemical test" in the second trimester of pregnancy is aimed at diagnosing trisomies - chromosomal pathologies in which an additional chromosome appears in the karyotype.

This test is carried out in order to identify women who have a very high risk of having a child with a chromosomal abnormality such as trisomy (Down's or Edwards's syndrome). For these women, further examination is recommended to confirm or completely exclude the indicated diseases in the fetus.

Indications for screening for trisomies in the 2nd trimester

Screening for trisomy is recommended for absolutely all pregnant women. However, some categories of women must undergo this examination without fail.

The indications are as follows:

  • the age of the pregnant woman is over 35;
  • the presence in the family of children with the mentioned syndromes;
  • burdened family history of any other hereditary diseases;
  • suspicion that one of the parents, before conception, was exposed to one of the mutagenic factors: radiation exposure or chemical poisoning.

Screening of the 2nd trimester should be carried out for a period of 15-20 weeks, the optimal time to donate blood for screening is 16-18 weeks.

Preparation for research

Before donating blood, fatty foods should be excluded from the diet within 24 hours. For 30 minutes, you should refrain from smoking, and also not worry.

How the research is done

The material for the study is the blood of a pregnant woman. With the help of immunochemiluminescence analysis, the level of the following substances in the blood is determined:

  • human chorionic gonadotropin (the abbreviation hCG is better known);
  • free estriol;
  • alpha-fetoprotein.

The examined woman, in addition to donating blood, must fill out a questionnaire, which reflects other parameters used to calculate the risk: age, race, the presence of chronic diseases and bad habits.

Interpretation of results


The results of the analyzes are processed using the "PRISCA" computer program, which gives the result. The calculations also take into account not only the test results, but also anamnestic data: the woman's age, race, the presence of severe diseases (diabetes mellitus or arterial hypertension), the presence of bad habits, etc.

The form of results indicates the likelihood of having a child with a particular pathology. For example, a result of 1: 300 suggests that one out of 300 women with similar results may have a child with a congenital pathology.

The indicator of the degree of risk is indicated for each of the pathologies separately:

  • Down syndrome (extra chromosome 21);
  • Edwards syndrome (extra 18 chromosome);
  • a neural tube defect (spina bifida or anencephaly).

Indicator 1: 100 or less - very high risk, 1: 1000 - high risk,<1:1000 низкий риск и <1:10000 – крайне низкий риск.

Additional Information

Patients should be aware that no diagnosis is made based on the PRISCA-2 test result! This indicator determines the subsequent tactics of examining a pregnant woman - she needs to undergo other, more invasive methods for diagnosing genetic and chromosomal pathologies. These methods include amniocentesis and cordocentesis, with the help of which fetal biomaterial is obtained for genetic research. These studies do not need to be completed if the screening examination and ultrasound showed no abnormalities.

The high estimated risk of having a child with a genetic pathology, calculated according to the PRISCA program (PRISCA), is not a reason for termination of pregnancy. The basis for abortion is not even a diagnosis confirmed with the help of genetic analysis - only a conscious choice of a woman can serve as a reason for terminating a pregnancy.

Literature:

  1. Kashcheeva T.K. "Prenatal biochemical screening - system, principles, clinical diagnostic criteria, algorithms"
  2. Order of the Ministry of Health of the Russian Federation dated December 28, 2000. No. 457 O improving prenatal diagnostics in the prevention of hereditary and congenital diseases in children (together with instructions for organizing prenatal examination of pregnant women in order to identify congenital and hereditary pathologies in the fetus, for conducting invasive diagnostics of the fetus and genetic research of cell biopsies).

General information about the study

Prenatal screening for trisomy II trimester of pregnancy is performed to assess the likelihood of the most common fetal abnormalities - trisomy 21 (Down's syndrome), trisomy 18 (Edwards syndrome), and neural tube defect between 14 and 22 weeks of gestation. Risk factors for developing such anomalies include childbirth over the age of 35, multiple pregnancies, obstetric history of fetuses with chromosomal abnormalities (trisomies 21, 13 or 18), concomitant HIV infection, IVF pregnancy, smoking, and diabetes ... Moreover, the mother's age is the most significant factor. Thus, the risk of developing fetal chromosomal abnormalities increases sharply after 35 years (1: 179 compared to 1: 476 in a 25-year-old woman).

Determination of AFP together with chorionic gonadotropin and estriol (the so-called triple test) at 15-20 weeks of pregnancy is used to screen for fetal developmental defects and chromosomal abnormalities. This screening test allows you to assess the likelihood of the presence of genetic diseases and malformations, but its result is not an absolute indicator of the pathology or normal development of the fetus.

Human chorionic gonadotropin (hCG) is produced in the fetal membrane of the human embryo. It is an important indicator of the development of pregnancy and its deviations. The hCG level reaches its maximum at the 10-11th week, and then gradually decreases. By this indicator, one can judge the successful course of pregnancy and identify fetal developmental disorders.

Alpha-fetoprotein is produced in the embryonic yolk sac, liver and intestinal epithelium of the fetus, its level depends on the state of the gastrointestinal tract, fetal kidneys and the placental barrier. He takes an active part in the full development of the fetus. In the mother's blood, its concentration gradually increases from the 10th week of pregnancy and reaches a maximum at 30-32 weeks. In this regard, AFP is used as a nonspecific marker of the state of the fetus and the presence of obstetric pathology.

Free estriol is the main estrogen of pregnancy and is of great importance for the normal development and functioning of the fetoplacental complex. Its concentration increases from the moment the placenta forms and grows progressively with the course of pregnancy. A low concentration of free estriol in combination with high levels of beta-hCG and alpha-AF is associated with an increased risk of intrauterine growth retardation and complications of the third trimester of pregnancy (premature placental abruption and preeclampsia).

It is very important to know exactly the gestational age of the fetus, as the levels of AFP, hCG and free estriol in the blood differ at different weeks of pregnancy.

In this screening study, the risk of pathologies is calculated using the PRISCA (Prenatal Risk Calculation) computer program developed by Typolog Software (Germany) and having an international certificate of conformity. For the study, the content of chorionic gonadotropin (hCG), alpha-fetoprotein (AFP) and unconjugated (free) estriol in the blood of a pregnant woman is determined.

Clinical data (age of the pregnant woman, body weight, number of fetuses, the presence and characteristics of IVF, race, bad habits, the presence of diabetes mellitus, medications taken) must be taken into account. If an ultrasound is performed, the gestational age is determined by its results, and not by the date of the last menstrual period.

After research and calculation of the risk of pathologies of the pregnant woman, a consultation with a doctor - obstetrician-gynecologist is appointed.

Screening results cannot serve as criteria for a diagnosis and a reason for artificial termination of pregnancy. On their basis, a decision is made about whether it is advisable to use invasive methods of examining the fetus. With a high risk, additional examinations are required, including cordocentesis, amniocentesis with a genetic study of the material obtained.

What is research used for?

  • For screening of pregnant women to assess the risk of fetal chromosomal abnormalities - Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), neural tube defect.

When is the study scheduled?

  • When examining pregnant women in the second trimester (the analysis is recommended for a period of 14 weeks 3 days - 22 weeks), especially in the presence of risk factors for the development of pathology:
    • age over 35;
    • history of miscarriage and severe complications of pregnancy;
    • chromosomal abnormalities, Down's disease or congenital malformations in previous pregnancies;
    • hereditary diseases in the family;
    • past infections, radiation exposure, taking in the early stages of pregnancy or shortly before it, drugs that have a teratogenic effect (can cause birth defects and fetal abnormalities).