At all times in the history of mankind, there have been cases of the birth of children with physical and mental pathologies caused by various genetic abnormalities. In the modern world, despite scientific progress, the causes of genetic failures in the human body are still not fully understood. But thanks to new discoveries in the field of medicine, one can now find out about the presence of pathology even before the birth of a child, and in some cases even before conception. It is a question of fetal karyotyping - an analysis by which a geneticist can recognize a genetic abnormality in an unborn baby.
The basics of human genetics
The human body consists of living cells, in the nuclei of which there are chromosomes - formations that contain, store and transmit hereditary information. The whole set of such formations, as well as their number, size and structure from the beginning of the twentieth century in genetics is called a karyotype.
Each healthy person is characterized by a set of 46 chromosomes, or of 23 pairs. Among them are distinguished:
- autosomes (contain and transmit by inheritance information on growth, color of eyes and hair, and so on, there are 22 pairs);
- sexual (the gender of a person depends on this pair: women have the same chromosomes in this pair, different for men).
During research in the 70s, all pairs of chromosomes were studied and numbered. It was accepted that the normal female karyotype is designated 46, XX, male - 46, XU chromosome. For each known chromosomal abnormality, the corresponding notation is also adopted.
The essence of the method of karyotyping
Half of the chromosomes are transmitted to the baby from the karyotype of the mother, the second half from the father. Therefore, even before the conception of a child, a couple can turn to geneticists to study their own karyotypes in order to understand how genetically compatible they are and to exclude possible abnormalities in the course of pregnancy or fetal development.
During pregnancy, if necessary, carry out karyotyping of the fetus. In the early stages, this procedure allows you to find out if the unborn baby has genetic defects.
Genetic analysis of the fetus, or prenatal karyotyping, requires intervention in the uterine cavity, and therefore this procedure cannot be called 100% safe. In order to avoid risk for mother and baby, if there is evidence, it is recommended to undergo an analysis of karyotypes before pregnancy.
Indications for analysis to future parents
Naturally, there is no need to visit geneticists for all couples who decide to conceive a child. There is a list of circumstances under which this is necessary.
Indications for the analysis of karyotypes of parents:
- age - one or both future parents over 35 years old;
- genetic pathologies in the genus of one of the spouses;
- female infertility of unknown etiology;
- history of several miscarriages or missed pregnancies;
- consanguineous relationship of spouses;
- hormonal failure in a woman;
- low fertilizing ability of male sperm;
- several unsuccessful attempts at in vitro fertilization (IVF);
- harmful working conditions for one or both parents;
- smoking, alcohol abuse, drug addiction partners;
- previously born children with genetic abnormalities.
If karyotyping is carried out in the presence of any of these factors, the analysis will help to verify the absence of chromosomal abnormalities in the unborn child.
Diagnostic preparation
If future parents still decided not to resort to fetal karyotyping, but to exclude a possible pathology at the stage of pregnancy planning, you will have to prepare for the analysis.
What you need to do before undergoing a genetic examination:
- give up bad habits (smoking, alcohol);
- treat all chronic diseases to prevent exacerbations;
- cure all acute inflammatory processes and other diseases;
- stop taking antibiotics, any other potent drugs.
The karyotype of future parents is examined on the basis of their venous blood, or rather, lymphocytes isolated from it. For several days, doctors observe their changes, analyze the quantity and structure. At the end of the procedure, the geneticist interprets the results, from which it becomes clear whether there is a threat of the birth of a baby with genetic anomalies.
In what cases do karyotyping of the fetus?
There are situations in which problems with infertility and bearing a child do not arise. But already during the onset of pregnancy, the attending physician may indicate the need for karyotyping of the fetus. In this case, the analysis is performed to detect chromosomal abnormalities directly in the unborn baby.
The need for analysis may arise in the case of:
- suspected fetal abnormalities on a routine ultrasound;
- previously born to a couple children with genetic diseases;
- mother's age in excess of 35 years;
- addiction to alcohol or drugs in the expectant mother (even in the past);
- deviations in the analysis of blood;
- unfavorable environmental conditions in the region where the couple lives;
- mother’s disease in the first trimester of pregnancy;
- harmful working conditions of both or one of the partners.
In the case of negative results of the analysis, the geneticist must report the likely risk to parents, explain the forecasts and options for the development of the situation. Even in the first three months of development, the presence of chromosomal abnormalities can be determined using molecular karyotyping of the fetus.
Determination of the frozen fetus karyotype
In addition to all of the above factors affecting the need for genetic studies of the unborn baby, the doctor may recommend karyotyping the fetus in an aborted pregnancy. This is done in order to determine the cause of the cessation of fetal development, as well as to help prevent a similar outcome in subsequent pregnancy.
Methods of genetic karyotyping
Many parents do not agree to undergo a genetic test, fearing for maintaining a pregnancy. In order to objectively assess the risks of analysis, it is necessary to understand the existing methods of fetal karyotyping.
Research Methods:
- Invasive. The most accurate method is carried out by penetrating the uterine cavity to collect tissue samples for analysis. Such an intervention causes the most concern, but they are justified only in 2-3% of cases, that is, according to statistics, no more than 3 out of 100 such procedures lead to miscarriage, amniotic fluid leakage, bleeding or placental abruption.
- Non-invasive It consists in comparing the results of ultrasound and biochemical analysis of the mother’s blood. This technique is absolutely safe for mother and baby, but cannot guarantee the correctness of the result. Basically, such studies show only% of the probability of having a baby with deviations.
In practice, the choice of method depends on the seriousness of the doctor's concerns. The presence of several factors influencing the presence of chromosomal pathologies speaks in favor of an invasive technique.
Analysis Steps
If at a planned appointment with a gynecologist it comes to karyotyping the fetus, how the analysis is taken is one of the first questions that a woman has. To conduct fetal chromosome research, genetic material is needed. Cord blood, chorionic villi and amniotic fluid are suitable for analysis. To obtain them, the doctor with a long needle penetrates through the abdominal wall into the uterine cavity. If we talk about the pain of the invasive method of fetal karyotyping, the reviews of women who passed through it speak more about unpleasant sensations than about pain.
There are two options for conducting a study:
- all pairs of chromosomes can be checked, but this will take more time (about two weeks);
- for 7 days, genetics examine chromosomal pairs, which may contain the causes of genetic abnormalities (13, 18, 21 pairs and sex chromosomes).
Thanks to the study of a pair of chromosomes responsible for the sex of the child, already in the early stages of pregnancy you can find out who to expect - a boy or a girl. But in view of the existing risks of the intervention, analysis is not recommended for this purpose only.
What pathologies can an analysis identify?
Modern medicine knows more than 700 pathologies caused by genetic abnormalities. Among them, the most common syndromes are:
- Down is the third chromosome in the 21st pair, the patient is characterized by mental retardation, features of appearance (short nasal bone, shortened skull, oblique section of the eyes, small auricles, short limbs and fingers, enlarged tongue, short thickened neck).
- Patau is an extra chromosome in the 13th pair, a serious pathology in the presence of which children rarely live more than 10 years.
- Edwards - trisomy in the 18th pair, characterized by defects in the cardiovascular system, there are also external defects (irregular shape of the skull, narrow eye section, small lower jaw).
- Shershevsky-Turner - there are no X chromosomes in a pair of sex chromosomes, the disease is characterized by low growth, joint deformation, insufficient puberty.
In addition to the listed syndromes, violations in the chromosome set of a child can provoke a number of other diseases, including:
- mental retardation;
- psychoses
- increased aggressiveness;
- malfunctioning of internal organs;
- idiocy;
- “cat scream” anomaly - in addition to congenital malformations, the pathology is characterized by prolonged angry crying of the child.
Unfortunately, genetic diseases are not treatable. The decision on the preservation of pregnancy, in the event of a pathology, should be made by future parents independently, without the slightest pressure from the medical staff.
Conducting analysis with aberrations
Aberrations are abnormalities in the number or structure of chromosomes. An analysis with aberrations is carried out not by the fetus, but by a woman who needs a more accurate examination, since a larger amount of biomaterial is taken to conduct it.
Such a need may arise if:
- alleged infertility;
- chronic miscarriage of pregnancy (more than 3 miscarriages, history of fading pregnancy);
- several failed IVF attempts.
A gynecologist does not prescribe a consultation with a geneticist and karyotyping without important reasons. Timely contact with specialists can help maintain the health of mother and baby.