Types of measurements
The probability of finding deviations depends on the type of measurements, called markers. There is no specific relationship inherent in a particular pathology, which forces several indicators to be taken into account:
- Heart defects
- Insufficient length of humerus and femur bones
- Increased thickness of the collar space
- No nasal bone
- Detection of a cyst in the choroid plexus.
Even if these markers are detected on an ultrasound, this does not confirm a chromosomal abnormality.
Does it make sense for older parents to be examined in advance?
Conventionally, the threshold age for chromosomal diseases in women is considered to be 35 years, when the risk begins to increase relatively quickly. This does not mean that all women over 35 will necessarily have a child with a genetic disease, but the likelihood is higher.
Men also have their own risks due to genetic changes, usually we are talking about the age over 45-50 years.
However, there is no point in undergoing any tests before planning a pregnancy.
Most of the time the changes I'm talking about are random. They occur in the reproductive cell of one of the parents at the time of conception and are in no way related to lifestyle or heredity.
If there is any hereditary disease in the family, it is worth consulting a geneticist when planning a pregnancy to determine whether future parents need laboratory testing and whether additional testing will be needed during pregnancy.
Screening Requirements
The effectiveness of ultrasound depends on the correctness of its implementation, namely compliance with certain conditions. Research in the first trimester of pregnancy should be carried out starting from the 11th week and no later than the 13th week.
When the baby is located in the uterus in such a way that it is difficult to make an adequate assessment of its condition, the woman is asked to perform certain actions: tapping on the stomach; coughing; minor movements. This is necessary for the fetus to change its position in the womb. Also, the method of performing ultrasound depends on the location, which can be done through the vagina or skin on the abdomen.
How screening is carried out during pregnancy: rules for performing the study
First of all, a woman needs to donate venous blood on an empty stomach for biochemical analysis. After blood collection, the pregnant woman undergoes an ultrasound scan performed by a doctor specializing in genetic research. The screening procedure is performed using high-class equipment.
Screening for Down syndrome can be performed transvaginally or abdominally. The first study is carried out by inserting a special attachment of an ultrasound machine into the vagina. 30 minutes before the examination, the woman needs to drink 500 ml of water. The second diagnosis is performed in the same way as the first. The only difference is that a pregnant woman does not need to drink large amounts of liquid. The third examination is performed abdominally and does not require special preparation.
After the procedure is completed, the doctor acquaints the pregnant woman with the results obtained. If screening indicators deviate from the norm, genetic consultation is recommended. In some cases, a slight deviation from normative values indicates the possibility of having a child with a pathology. Compliance of the results with the standards is an indicator of the healthy progression of pregnancy.
What tests are included in screening?
A comprehensive diagnosis of downism during pregnancy includes a blood test and ultrasound diagnostics. During gestation, the protein component of the blood changes in the body. There is a connection between blood components and the presence of developmental abnormalities in the child. A change in protein levels accompanies a normal pregnancy, so medical specialists take into account the period at which the study is carried out.
Ultrasound examination includes examination of the fetal collar zone. Each child has a small amount of fluid in this area, the level of which can be determined using ultrasound. There is a relationship between fluid levels and the risk of having a child with Down syndrome. The discovery of swelling during the study of the collar space indicates the likelihood of downism and heart defects.
The study of body systems using ultrasound radiation allows us to identify structural abnormalities of the fetus. The study is able to detect some possible defects. The degree of diagnostic accuracy depends on the type of test, the experience of the medical specialist and the equipment.
When is the examination done?
Screening is carried out once every trimester. The first examination is performed in the first trimester of pregnancy, more precisely at 11-13 weeks; diagnosis at a longer period is uninformative. The biochemical test is aimed at clarifying the level of hCG and PAPP-A. This analysis is called the “Double Test” and allows you to find out the likelihood of having a child with Down and Edwards disease. Screening using ultrasound equipment and a biochemical test make up a comprehensive triple test for the first period of pregnancy.
Screening examinations during pregnancy in the second trimester are performed between 16 and 18 weeks. At this stage, it is possible to measure a larger number of indicators than in the previous period. Biochemical diagnostics can identify abnormalities in the structure of the spine, anencephaly, downism, and Edwards syndrome. A combined examination of the second trimester combines a biochemical test and ultrasound.
At 32-34 weeks, the third screening is carried out, including an ultrasound examination of the fetus, recording the baby’s heart rate, and Doppler measurements. A set of diagnostic methods is used to assess the general condition of the fetus.
Signs indicating the presence of an anomaly
A specialist is able to diagnose Down syndrome during the study if the pregnancy period is 11–13 weeks. The most significant indicator in determining this pathology is the thickness of the collar zone. If the nuchal space in the photo is thinner than 3 mm, then the risk of a chromosomal abnormality is extremely high.
In addition to determining the thickness of the cervical fold, diagnosing the syndrome is possible using other parameters. Particular attention is paid to the structure of the brain and pelvis of the fetus. If a chromosomal abnormality is noted, then you can see in the photo hypoplasia of the cerebellum, its significant reduction in size along with the frontal lobe. When it is possible to detect on ultrasound a simultaneous decrease in the size of the thalamic frontal distance and the cross-section of the cerebellum, then with a high probability it can be stated that the syndrome is present.
An increase in the angle between the ilia with a simultaneous decrease in their length will serve as evidence of an anomaly. The indicator is measured in the cross-sectional area of the middle of the sacrum.
Risk percentage
Regardless of the identification of certain symptoms, it is difficult to talk about the presence of a syndrome. We are talking only about the risk that increases as a percentage with certain signs. For example, the absence of new bone in 70% of cases is evidence of pathology, but 2% of children, despite this, are born healthy. Detection of blood flow disturbances in the venous ducts in 80% of cases confirms the anomaly, but 5% of newborns who had such abnormalities by the 11th week are born normal.
The following abnormalities also confirm Down syndrome:
- Enlarged bladder
- Tachycardia
- Absence of one of the umbilical arteries.
These signs in themselves are never confirmation of anomalous phenomena and require additional research.
Step-by-step ultrasound examination during pregnancy
The Ministry of Health of the Russian Federation issued Order No. 457, according to which women are required to undergo ultrasound examinations three times during pregnancy. The first study is carried out no later than the 13th week, the second at the 24th week, and the third time at the 34th week. This is due to the need to control growth dynamics; the older the fetus, the more likely it is to identify obvious symptoms of an anomaly.
First screening
During each screening, certain tasks are set, in particular, at the 13th week they try to detect the presence of chromosomal pathology.
The anatomical structure is assessed to identify characteristic developmental defects. Detection of a chromosomal abnormality with a high degree of certainty will make it possible to take preventive measures, for example, if it is decided to have an abortion, it will take place with minimal consequences for the health of the mother. However, at this stage it is impossible to find all the defects characteristic of Down syndrome, that is, it is certainly premature to say about its absence at this stage, even taking into account biochemical screening.
Second screening
Conducting a study at week 24 will be more informative and will allow a detailed study of the structure of the fetus. Three types of defects can be identified here:
- Cleft lip
- Central nervous system disorder
- Heart defects.
Ultrasound examination does not give a complete picture even in this case, that is, there is no guarantee of the absence of an anomaly. Only visualization of large defects of the heart muscle is available, but a minor degree of pulmonary trunk stenosis cannot be diagnosed. The syndrome at this stage of screening is determined by the location and thickness of the placenta, as well as the volume of amniotic fluid present.
Modern ultrasound technologies guarantee the production of planar two-chamber and three-dimensional three-chamber images. Each of the methods is effective in its segment, for example, superficial defects: facial defects; spina bifida - detected using a three-chamber method. Defects characteristic of internal organs are determined by a two-chamber study. The second anatomical ultrasound is performed within 45 minutes.
Third stage
The third stage, carried out at the 34th week, is also important, because there is a small group of defects that appear after a second examination. There are several reasons for this:
- Fetal position does not allow accurate visualization of abnormalities
- Small volume of amniotic fluid
- Large body weight of a woman
- The defect does not manifest itself clinically.
You can do without the third stage, for example, in the USA, local doctors consider only the first two studies mandatory. Pregnant women are allowed to neglect it, for whom the second screening fully reveals the picture and there is a guarantee that Down syndrome does not threaten the child.
How does Down syndrome manifest after birth?
This pathology is chromosomal, that is, associated with improper formation of the material from which chromosomes are composed. In this case, the 21st pair suffers. Complete or partial copying of a 21-pair chromosome results in the formation of extra material carrying excess genetic material (trisomy instead of two chromosomes). Therefore, a sick child has 47 chromosomes, and not the normal number of 46. The presence of an additional chromosome with excess genetic material determines the process of fetal development, which occurs with some deviations characteristic of this pathological syndrome.
As a result, a newborn child with Down syndrome immediately attracts the attention of obstetricians and neonatologists (specialist doctors in the neonatal period who work in maternity hospitals). Trisomy 21 chromosome pairs manifests itself with a characteristic clinical picture. From the entire complex of signs, several of the most typical and striking external symptoms can be identified. This is a small skull, a flat nose, a very short neck with a skin fold, and an oblique eye shape due to an extra fold of skin. A long and deep transverse groove is clearly visible on the baby’s palms; the little finger is curved and often underdeveloped. There are other characteristic symptoms throughout the body of a child with Down syndrome.
Risk system
How high the likelihood of a fetus having the syndrome is determined using a special scale. There is a risk system; if they exceed 1:380, then the woman is sent for additional examination. There are the following types of risks: high; short; average. If the data on the scale exceeds 1:200, then there is a high probability that the syndrome will be diagnosed.
A result of 1:3001 is considered satisfactory and no additional tests are required. An unscheduled ultrasound is recommended for average risk, when the result is between 1:201 - 1:3000. In this case, signs indicating the presence of Down syndrome are detected, but they should be confirmed, for which an ultrasound examination is prescribed at the 16th week.
If a woman is at risk, what should she do?
If the risk according to the results of ultrasound and biochemical studies is high, we suggest coming for a consultation with a geneticist.
According to the results of studies of the 1st trimester, an average of 4% of women are at risk.
We offer them invasive procedures, such as amniocentesis, where amniotic fluid is taken for examination. Thus, we obtain cells in which we examine the set of fetal chromosomes and can give an answer whether the child has a chromosomal disease or not.
Tests must be monitored in advance - blood and urine tests, a smear is taken, if there are contraindications, amniocentesis is not prescribed or is carried out after treatment and repeated control of tests. The procedure for collecting amniotic fluid is done under ultrasound guidance. After the procedure, the woman has the opportunity to lie down and relax.
