Screening of the second trimester: when done, interpretation of the results, indicators of the norm and deviations. Routine second trimester screening

Biochemical screening is a study of the blood of a pregnant woman to determine specific markers that help determine the likelihood of a severe genetic disorder in the fetus.

From the moment of its formation, the placenta begins to produce certain substances, which then penetrate into the mother's blood. The amount of these markers normally changes constantly as the fetus develops. The determination of these substances is the basis of biochemical screening: significant deviations of the results obtained from the accepted norms indicate a high possibility of the presence of chromosomal abnormalities or.

information Of course, such laboratory tests cannot make a diagnosis, but they help to select a group of women at high risk of having children with pathology and offer them further in-depth examination to clarify the situation.

Biochemical screening is performed twice during the entire period of gestation: in the first trimester (10-14 weeks) and in the second trimester (16-20 weeks).

Indications for

The question of the need to perform biochemical screening in all pregnant women is still controversial. Most experts recommend doing this test to all patients, because no one is immune from genetic disorders. The World Health Organization (WHO) recommends at least compulsory laboratory tests in all pregnant women.

This analysis is optional, and the decision to perform is voluntary for every expectant mother, although, of course, it will not hurt to insure yourself once again.

In addition, groups of women have been identified who have a high risk of having children with genetic pathology. Such patients should be examined twice during the entire period of gestation.

At-risk groups requiring mandatory biochemical screening:

• The age of a woman is over 30 for the first pregnancy and over 35 for the second and subsequent;
• 2 or more history of spontaneous abortion;
• Self-administration of drugs in the early stages, which have a teratogenic effect;
• Infectious diseases transferred in the first trimester;
• The presence in the family of relatives with genetic abnormalities;
• The presence of genetic abnormalities in one or both parents;
• The birth of a child with genetic abnormalities earlier in the family;
• Stillbirth or death of another child from developmental defects in the family earlier;
• Marriage between close relatives;
• Radiation exposure to one or both parents before conception or early in pregnancy;
• Deviations found on ultrasound of the fetus.

First biochemical screening

Biochemical screening of the 1st trimester is performed at 10-14 weeks, however, most experts consider it more informative to conduct a study at 11-13 weeks.

The first screening is a "double test", i. E. two substances are determined in the blood: (in particular, a free unit of human chorionic gonadotropin) and PAPP-A (plasma protein A associated with pregnancy).

Norms

Chorionic gonadotropin is secreted by the cells of the chorion (shell of the embryo), therefore, it begins to be determined in the blood quite early (already in the first days after the conception occurred). Further, its amount gradually increases, reaches a maximum by the end of the first trimester, then begins to decline and from the second half of pregnancy remains at a constant level.

Normal levels of hCG

RAPP-A Is a protein produced by trophoblast throughout the entire period of gestation, its amount increases constantly in proportion to the gestational age.

Normal indicators of PAPP-A

Pregnancy period, weeks	Normal indicators of PAPP-A, mU / ml
	Minimum value	Maximum value
8-9	0.17	1.54
9-10	0.32	2.42
10-11	0.46	3.73
11-12	0.7	4.76
12-13	1.03	6.01
13-14	1.47	8.54

additionally The result of biochemical screening is assessed not only by the results obtained, but also by the value of MoM, which ultimately is the determining factor. MoM is a coefficient showing the degree of deviation of the obtained indicator from the average normal indicator for a given gestational age. The MoM rate is from 0.5 to 2.5 (with multiple pregnancies up to 3.5 MoM).

Decryption

Deciphering biochemical screeningshould only be performed by the attending physician. It should be borne in mind that each laboratory, depending on the reagents used, may have its own performance standards, in this regard, using incorrect data, you can get false results.

Decoding the analysis for hCG

Deviations of the indicator from the norm	Causes
Decreased hCG levels
	Delayed development of the embryo
	High risk of spontaneous miscarriage
	Fetal Edwards syndrome
Elevated hCG levels	Multiple pregnancy
	Severe toxicosis
	Diabetes mellitus in the mother
	Down syndrome in the fetus
	Severe malformations in the fetus (cardiovascular, nervous systems and others)
	Taking progestational drugs (,)
	Malignant diseases (cystic drift, chorionic carcinoma)

Decoding analysis on PAPP-A

Biochemical screening in the second trimester

Biochemical screening of the 2nd trimester consists of a "triple test": determination of AFP (alpha-fetoprotein), hCG and free estriol. The analysis is performed from 16 to 20 weeks, but the most informative examination will be at 16-18 weeks.

Norms of the "triple test"

AFP- a protein produced in the gastrointestinal tract and liver of the fetus from the early stages of its development.

Normal AFP readings

Normal levels of hCG

Free estriol Is a hormone produced initially only by the placenta, and then by the baby's liver. During the normal course of pregnancy, the amount of free estriol is constantly increasing.

Normal values ​​of free estriol during pregnancy

Decryption

2 biochemical screening should also be deciphered only by the attending physician, taking into account the standards of this laboratory.

Decoding analysis for AFP

Deciphering the analysis for free estriol

Screening of the 2nd trimester of pregnancy is a set of measures aimed at identifying possible pathologies in the fetus. It consists of an ultrasound examination and the so-called "triple test" (biochemical screening of the 2nd trimester). You can go through it between 14 and 20 weeks, but the optimal period is considered to be 16-18 weeks of pregnancy.

How is the 2nd trimester screening going?

This is an additional study, but it does not have any special indications for its appointment. So do not be surprised if your doctor recommends 2 trimester screening - ultrasound and biochemical analysis. You can refuse both an ultrasound scan and an analysis, which, by the way, is paid in most cases. But still, in modern conditions, women often try to go through the maximum complex of diagnostics.

First, an ultrasound examination is performed. It will give a general understanding of the state of the fetus, the formation of its main systems. Ultrasound also helps to more accurately determine the period, which is very important when decoding the 2nd trimester screening - the norms are set strictly for each period of pregnancy. After that, it is important not to hesitate to donate blood for the "triple test". Blood is taken from a vein and on an empty stomach, preferably the next day or in the days following the ultrasound scan. Biochemical screening for the 2nd trimester is aimed at determining the level of three specific substances in the blood:

• Human chorionic gonadotropin - hCG, by which most women learn about pregnancy using home rapid tests;
• Alpha-fetoprotein - AFP, a protein that is produced in the body of the fetus and is responsible for protecting it from a possible threat from the mother's immunity;
• Free (unconjugated, unbound) estriol is a steroid hormone, the main estrogen of pregnancy, necessary for normal metabolism in the mother-child system.

Transcript of 2nd trimester screening

According to the blood test, quantitative indicators are derived for all three test substances. Derived conditional norms for each gestational age.

Screening rates for the 2nd trimester are as follows:

• 16 weeks - 10,000-58,000 mU / ml;
• 17-18 weeks - 8,000-57,000 mU / ml;
• 19 weeks - 7,000-49,000 IU / ml.

Chorionic gonadotropin is usually measured in special units - mU / ml, they are also mMe / ml. Some laboratories use measurements in nanograms - ng / ml. 1 ng = 1 honey: 21.28.

• 12-14 weeks - 15-60 U / ml;
• 15-19 weeks - 15-95 U / ml;
• 20-24 weeks - 27-125 U / ml.

• 13-14 weeks - 5.7-15 nmol / l;
• 15-16 weeks - 5.4-21 nmol / l;
• 17-18 weeks - 6.6-25 nmol / l;
• 19-20 weeks - 7.5-28 nmol / l;
• 21-22 weeks - 12-41 nmol / l.

In addition to these data, the average MoM coefficient is displayed - the ratio of indicators. Normally, MoM fluctuates in the range of 0.5-2.0.

Is 2 trimester screening necessary?

The first step is to emphasize that this research is unnecessary. The test results are unreliable and do not make it possible to make a diagnosis - only assumptions can be made from these data. The fact is that biochemical screening of the 2nd trimester can only indicate a certain probability of the presence of pathologies in the fetus. So if, according to the ultrasound data, everything is normal, then this is just an additional confirmation. If screening was done in the first trimester, and its results did not cause concern, then your doctor is unlikely to insist on re-diagnosis.

The decision on whether to undergo screening for the 2nd trimester or not is up to the woman at her own discretion. They recommend it to everyone, without exception, since pathology can appear for no apparent reason, out of nowhere. So many go through this study in order to calm themselves in advance, getting rid of one of the worries about the health of their unborn baby. Others, clearly realizing that they will not terminate the pregnancy under any pretext, deliberately refuse this diagnostic method. However, a lot of worries are experienced by those women whose blood counts did not fit into the 2nd trimester screening standards.

What if the 2nd trimester screening results are abnormal?

The main thing is not to panic! Whatever deviations from the norm, it still does not mean anything. Moreover, there are often cases when, despite the frankly frightening indicators, completely healthy babies are born. Unfortunately, it also happens the other way around - with perfect analyzes, things don't go so smoothly in the end. That is, the data obtained may well be false negative or false positive - the truth of the test does not exceed 70%.

The doctor, based on your specific case, will try to reassure you by pointing out the presence of factors that influenced the results of the 2nd trimester screening. And there are a lot of them: colds, mother's diabetes, low or overweight, smoking, taking medications, especially pregnancy (not pathology), etc. So if ultrasound did not show anything suspicious during the screening of the 2nd trimester, then biochemical data are not taken into account ... Although you may well be sent for a consultation with a geneticist, it is unlikely that you will be able to get a specific answer from him - only assumptions.

In case of serious suspicion, it is proposed to continue the diagnosis with more serious methods. Unfortunately, they also cannot give an accurate result, but at the same time they take a lot of time and are fraught with a number of pregnancy complications (up to a miscarriage). And in the end, after all this mental anguish, you may get another one - an offer to have an abortion at the fifth or even sixth month of pregnancy, relying on unreliable research results. In addition to the moral and psychological aspect, such intervention also significantly affects the physiology, posing a threat to a woman's health. 4.6 out of 5 (45 votes)

Study Information

Prenatal (antenatal) screening is a comprehensive medical study (laboratory and instrumental) aimed at identifying a risk group for the development of fetal chromosomal abnormalities during pregnancy. The results of the screening make it possible to make a decision on the need for a more detailed examination (invasive diagnosis, consultation of a geneticist).

"Laboratory Hemotest" performs prenatal screening for the second trimester of pregnancy using PRISCA (PrenatalRiskCalculation) software from Siemens Healthcare Global. To calculate the biochemical risk of chromosomal abnormalities, the program uses indicators of biochemical blood markers, anthropometric data of the fetus based on the results of ultrasound examination, as well as the personal data of the pregnant woman.

Prenatal screening II trimester:

• It is carried out in terms of 14-20 weeks of pregnancy;
• Biochemical (serum) markers: alpha-fetoprotein (AFP), chorionic gonadotropin (hCG), free estriol, free β-hCG;
• Ultrasound data of the II trimester with the date of completion: biparietal fetal size (BPD) for calculating the gestational age;
• Personal data of a pregnant woman: age, weight, race, bad habits (smoking);
• Anamnesis of a pregnant woman: the number of previous pregnancies, the presence of multiple pregnancies, in vitro fertilization, the presence of diseases (insulin-dependent diabetes mellitus).

To correctly calculate the risk of developing chromosomal abnormalities, the laboratory must have accurate data on the gestational age, ultrasound data (CTE, TVP and imaging of the nasal bone for the first trimester) and complete information about all the factors necessary for screening (indicated in the direction form). The gestational age can be calculated by the date of the last menstrual period (LMP), the date of conception (estimated period). For prenatal screening, it is recommended to use a more accurate and informative method - calculating the gestational age according to ultrasound data (CTE and BPD). Due to the existence of several statistical methods for determining the gestational age according to fetal ultrasound data, the calculation results performed using the PRISCA software may slightly differ from the gestational age established by the ultrasound doctor (range up to 7 days in the II trimester).

The PRISCA analysis software allows you to:

• calculate the likelihood of various risks of fetal pathology
• take into account the individual data of the patient
• take into account the factors influencing the detection of deviations from normal levels of biochemical markers.

Screening parameters in the 2nd trimester (14-20 weeks):

• Ultrasound measurement of BPD (Biparietal size) 26-56 mm. (limitation period 1-3 days)
• Immunochemical determination 1) beta-hCG - free and total, 2) AFP, 3) free estriol.

Risk calculation features:

• The risk calculation depends on the accuracy of the data provided for the analysis.
• The calculation of risk is the result of statistical processing of the data.
• The results should be confirmed (or excluded) by cytogenetic studies.

The result is presented in the form of MoM- this is the deviation of the indicators of this pregnant woman from the average norm
Beta-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 maximum level of beta-hCG reaches 10-11 weeks, and then gradually decreases. An increase in the concentration of beta-hCG in pregnant women in the second trimester of pregnancy may indicate a risk of developing trisomy on chromosome 21 (Down's syndrome) in the fetus. A decrease in the concentration of the hormone may indicate the development of other chromosomal abnormalities in the fetus, in particular Edwards syndrome, trisomy on the 18th chromosome.

Alpha-fetoprotein (AFP)- 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. In the mother's blood, its concentration gradually increases from the 10th week of pregnancy and reaches a maximum at 30-32 weeks. A decrease in concentration is observed in Down syndrome. With a neural tube defect, the AFP level rises.

Free estriol- is produced by the placenta, and then by the liver of the fetus. It stimulates the synthesis of vasodilating prostaglandins in endometrial cells and increases uteroplacental blood flow. In addition, it increases the receptor-mediated uptake of low-density lipoprotein cholesterol for the subsequent synthesis of progesterone by the placenta, and also stimulates the growth of the mammary gland. In Down syndrome and Edwards syndrome, the concentration of free estriol decreases. Also, the level of the hormone may decrease due to the intake of drugs: dexamethasone, prednisolone, metipred, antibacterial. A low concentration of free estriol in combination with high levels of beta-hCG and AFP is associated with an increased risk of intrauterine growth retardation and complications of the third trimester of pregnancy (premature placental abruption and preeclampsia).

In accordance with the order of the Ministry of Health of the Russian Federation dated 01.11.2012, No. 572n. The procedure for the provision of medical care in the field of "obstetrics and gynecology (except for the use of assisted reproductive technologies)": it is necessary to conduct prenatal screening of the II trimester at a gestational age of 18-20 + 6 weeks.

If, for some reason, ultrasound was not performed in the II trimester, you can provide data (CTE, TVP, nasal bone imaging) of the I trimester ultrasound with the date of completion. Calculating the risk of developing chromosomal abnormalities in the second trimester using ultrasound data of the first trimester has less accuracy and greater error compared to using ultrasound data of the second trimester.

Algorithm for prenatal screening and II trimester of pregnancy:

1. Calculate the gestational age by the date of the last menstruation or the day of conception and determine the date of the ultrasound scan and blood donation for biochemical markers.
2. Conduct an ultrasound scan. If the ultrasound data are not suitable for calculating the risk (CTE<38мм), провести повторное выполнение УЗИ только по рекомендации врача через определенное время.
3. Knowing the exact duration of pregnancy, calculated by ultrasound, carry out blood sampling for studies of biochemical markers. The time interval between the ultrasound scan and blood donation should be minimal (no more than 2-3 days).

Attention! Medication can affect your prenatal screening results!

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:

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 at 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.

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

Training

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.