What is a karyotyping test?
A karyotype is a complete set of chromosomes (that is, structures in which hereditary information about a wide variety of features is located). In the human body, there should be 46 of them: 22 pairs of autosomes, which are responsible for the transmission of certain characteristics to the children and 1 pair of sex chromosomes.
Karyotyping is a study that allows to study in detail the chromosome set and identify possible disorders.
Indications for karyotyping of spouses
Some changes in the set of chromosomes are often the cause of infertility, miscarriage or the birth of a child with various syndromes.
It is necessary for spouses to take this test at the stage of pregnancy planning if:
- pregnancy does not occur during the year of regular sexual activity after complete cancellation of contraception. In this case, the study will help clarify the causes of infertility;
- there were 2 or more miscarriages in the history;
- there was a still pregnancy in the history;
- there were cases of stillbirth or death of a child under the age of 1 year;
- there already is a child with chromosomal abnormalities in the family;
- according to the results of the spouse's spermogram, non-obstructive azoospermia (complete absence of germ cells in the ejaculate, and it’s not caused by obstruction of the vas deferens) or severe oligozoospermia (a significant decrease in the concentration of gametes) was revealed;
- amenorrhea (absence of menstruation for six months or more) in the spouse;
- there are relatives of husband or wife with chromosomal abnormalities.
Although the chromosome set of a person does not change during life, defects may appear over the years due to external factors (so-called irregular aberrations).
Preparation for karyotyping
For research, venous blood is taken. To prepare for the test patients need to follow some recommendations.
Usually, the karyotype test (unlike many other tests) is not performed on an empty stomach. It is advisable to donate blood 1.5-2 hours after a meal.
2 weeks before the analysis, you must stop taking antibacterial drugs.
The study will need to be postponed if an acute disease or exacerbation of a chronic disease occurs.
Types of diagnostics
For performing classical cytogenetic analysis venous blood is taken, from which, on average, up to 15 lymphocytes are extracted (but depending on the laboratory, country and other individual requirements, the amount of extracted cells can be from 6 to 100). Then they are cultivated for several days. During the study, the chromosomes are colored, so the individual striation of each of them becomes visible, and is carefully studied.
If necessary, a geneticist can recommend additional methods:
- spectral karyotyping (SKY);
- fluorescent hybridization (FISH).
How to decrypt the test results
Normally, the results of karyotyping are as follows:
- 46XX (female karyotype);
- 46XY (male karyotype).
In addition, a mosaic karyotype can be detected when pathological changes appear only in some cells, while others do not have any abnormalities (for example, 45,X/46, XX).
The analysis can detect such disorders as:
- trisomy, when an extra copy appears in a pair of chromosomes;
- monosomy, when a pair is missing one of the chromosomes. For example, Shereshevsky-Turner syndrome, in case of which the karyotype most often has the form 45,X.
Among possible disorders, such disorders as duplications (doubling), deletions (losses), translocations (moving) and inversions (twists) of chromosome sections should be also mentioned.
What should I do if abnormalities are detected?
Only a qualified geneticist can correctly determine the nature of the identified disorders and develop optimal tactics.
In some cases, anti-mutagenic therapy is recommended to reduce the number of mutations.
In addition, during pregnancy planning, your doctor may recommend preimplantation genetic testing (PGT) as part of an in vitro fertilization program. In this case, embryos that were obtained in IVF program are examined for the presence of chromosomal abnormalities, after examination only embryos that do not have such disorders are transferred into the patient's uterus.
Fact about karyotyping
Often, karyotyping reveals chromosomal abnormalities that do not have any visible signs, but can cause a decrease of reproductive function, miscarriage and the birth of a sick child.