Fetal karyotype in humans is a combination of the signs of its chromosomal set. A human chromosome is 46, 22 of them are autosomes and a pair of sex chromosomes. To determine the human karyotype, its cells are used, staining them with dyes, photographing and examining the chromosomes by microscopy. At the same time, the number of chromosomes, their sizes and morphological features are studied. A number of chromosomal diseases can be diagnosed by the change in the number of chromosomes (especially sexual chromosomes), or by any other intrachromosomal and interchromosomal rearrangements.
How do karyotyping of the fetus?
Prenatal karyotyping of the fetus is necessary for the diagnosis of chromosomal diseases. For this, fetal cells are needed: chorion villi or amniotic fluid.
A complete or partial examination of the fetal karyotype can be performed. At full research, the whole set of chromosomes of the fetus is analyzed, but the study time is quite long - 14 days. And with a partial study for 7 days, only those chromosomes, problems in which indicate genetic diseases ( Down's Syndrome , Patau or Edwards). Usually it is 21, 13, 18 pairs of chromosomes and sex chromosomes.
Study of sex chromosomes
Many parents want to know the gender of the child before the birth, and ultrasound does not always show this reliably, but karyotyping determines the sex very accurately. But karyotyping with the study of sex chromosomes is not done at all for this. Normal fetal carotid 46 XX is a karyotype of a girl, but if the X chromosome is more than two (most often 3 is trisomy X, or more than 3 is polysomy X), then this is the risk of mental retardation, psychosis. But monosomy X (one X-chromosome) is a karyotype of the Shershevsky-Turner syndrome.
Normal fetal karyotype of 46 XY is a karyotype of a boy. But a child with a karyotype of XXU (polysomy of the X chromosome in men) will be born with Klinefelter's syndrome, and a boy with polysomy on the Y chromosome will have high growth, some mental retardation and increased aggression.
Indications for fetal karyotyping
Indications for prenatal karyotyping are:
- the age of parents older than 35, their blood relationship;
- in this family there are already children with malformations or there were frozen pregnancies of children with malformations, spontaneous miscarriages, interruption of pregnancy due to the identification of incompatible fetal developmental anomalies;
- harmful working conditions and parents' lives, bad habits (drug addiction or alcoholism);
- viral diseases in the first trimester of pregnancy;
- suspicions of congenital diseases with ultrasound investigation in 1 and 2 trimester of pregnancy.