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, it is now possible to find out about the presence of a pathology even before the birth of a child, and in some cases even before his conception. We are talking about fetal karyotyping - an analysis through which a geneticist can recognize a genetic abnormality in an unborn baby.
Fundamentals 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 entire set of such formations, as well as their number, size and structure, has been called a karyotype in genetics since the beginning of the 20th century.
For each he althy person, a set of 46 chromosomes, or 23 pairs, is characteristic. Among them are distinguished:
- autosomes (contain and inherit information about height, eye and hair color, and so on, there are 22 pairs of them);
- sexual (the sex of a person depends on this pair: women in this pair have the same chromosomes, men have different chromosomes).
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,XY chromosome. Each known chromosomal abnormality is also labeled accordingly.
The essence of the karyotyping method
Baby half of the chromosomes are transmitted from the karyotype of the mother, the other half from the father. Therefore, even before conceiving a child, a couple can turn to geneticists to study their own karyotypes in order to understand how genetically compatible they are, to exclude possible anomalies 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 future baby has genetic defects.
Fetal genetic analysis, or prenatal karyotyping, requires intervention in the uterine cavity, and therefore this procedure cannot be called 100% safe. Pre-pregnancy karyotype testing is recommended to avoid risk to mother and baby if indicated.
Indications for analysis by future parents
Of course, there is no need to visit geneticists for all couples who decide to conceive a child. There is a list of circumstances in whichmake it necessary.
Indications for parental karyotype analysis:
- age - one or both future parents over 35;
- genetic pathologies in the family of one of the spouses;
- female infertility of unknown etiology;
- several miscarriages or missed pregnancies in history;
- consanguinity of spouses;
- hormonal failure in a woman;
- low fertility of male sperm;
- several unsuccessful in vitro fertilization (IVF) attempts;
- harmful working conditions for one or both parents;
- smoking, alcohol abuse, drug addiction partners;
- previously born children with genetic abnormalities.
If, in the presence of any of these factors, a karyotyping is performed, the analysis will help to make sure that there are no chromosomal abnormalities in the unborn child.
Preparing for diagnostics
If future parents still decide not to resort to fetal karyotyping, but to exclude possible pathology at the stage of pregnancy planning, you will have to prepare for the analysis.
What needs to be done before undergoing a genetic examination:
- give up bad habits (smoking,alcohol);
- treat all chronic diseases to prevent flare-ups;
- cure all acute inflammatory processes and other diseases;
- stop taking antibiotics, any other strong 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 their 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 abnormalities.
When is fetal karyotyping performed?
There are situations in which there are no problems with infertility and childbearing. But already during the onset of pregnancy, the attending physician may indicate the need for fetal karyotyping. In this case, the analysis is carried out to detect chromosomal disorders directly in the unborn baby.
The need for analysis may arise in the case of:
- Suspicion of fetal anomalies on planned ultrasound;
- children previously born to a couple with genetic diseases;
- mother's age over 35;
- dependence on alcohol or drugs in the expectant mother (even in the past);
- abnormal blood tests;
- unfavorable ecological situation in the region where the couple lives;
- mother's illness in the first trimester of pregnancy;
- harmful working conditions of both or one of the partners.
In the event of negative test results, the geneticist must inform the parents about the likely risk, explain the forecasts and options for the development of the situation. Even in the first three months of development, molecular karyotyping of the fetus can determine the presence of chromosomal abnormalities.
Determining the karyotype of a frozen fetus
In addition to all of the above factors that affect the need for genetic testing of the unborn child, the doctor may recommend karyotyping of the fetus during a missed 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 a subsequent pregnancy.
Methods of genetic karyotyping
Many parents do not agree to a genetic analysis, fearing for the continuation of the pregnancy. 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 performed by penetrating into the uterine cavity to take 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. Is incomparison of the results of ultrasound and biochemical analysis of the mother's blood. This technique is absolutely safe for mother and child, but cannot guarantee the correctness of the result. Basically, such studies show only a % chance 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 that influence the presence of chromosomal abnormalities speaks in favor of an invasive technique.
Analysis steps
If at a scheduled appointment with a gynecologist it comes to fetal karyotyping, how the analysis is taken is one of the first questions a woman has. To conduct a study of the chromosomes of the fetus, genetic material is needed. Cord blood, chorionic villi and amniotic fluid are suitable for analysis. To obtain them, the doctor, using 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 have gone through it speak more of discomfort than pain.
There are two options for conducting research:
- you can check all pairs of chromosomes, but it will take more time (about two weeks);
- for 7 days, geneticists examine chromosome pairs that may contain the causes of genetic abnormalities (13, 18, 21 pairs and sex chromosomes).
Thanks to the study of the pair of chromosomes responsible for the sex of the child, already at an early stage of pregnancy, you can find out who to expect - a boy or a girl. But given the risksconducting an intervention, it is not recommended to analyze for this purpose only.
What pathologies can the analysis reveal?
Modern medicine knows more than 700 pathologies caused by genetic abnormalities. Among them, the most common syndromes are:
- Down - the third chromosome in the 21st pair, the patient is characterized by mental retardation, features of appearance (short nasal bone, shortened skull, oblique cut 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, defects in the cardiovascular system are characteristic, external defects are also present (irregular shape of the skull, narrow eye section, small lower jaw).
- Shershevsky-Turner - there is no X chromosome in the pair of sex chromosomes, the disease is characterized by short stature, deformity of the joints, insufficient puberty.
In addition to the above syndromes, disorders in the chromosome set of a child can provoke a number of other diseases, including:
- mental retardation;
- psychosis;
- increased aggressiveness;
- disorders of internal organs;
- idiocy;
- anomaly "cat's cry" - in addition to congenital malformations, the pathology is characterized by prolonged hysterical crying of the child.
Unfortunately, genetic diseasesnot amenable to treatment. The decision to preserve the pregnancy, in the event of a pathology, should be taken by the future parents on their own, without the slightest pressure from the medical staff.
Analyzing with aberrations
Aberrations are called abnormalities in the number or structure of chromosomes. Analysis with aberrations is performed not on the fetus, but on a woman who needs a more accurate examination, since a larger amount of biomaterial is taken for it.
Such a need may arise in the case of:
- presumed infertility;
- chronic miscarriage (more than 3 miscarriages, history of pregnancy fading);
- several failed IVF attempts.
A gynecologist does not prescribe a consultation with a geneticist and karyotyping without important reasons. Timely access to specialists can help maintain the he alth of mother and child.
