The most common genetic disorders that can occur are differences in chromosome number. The biggest chromosomal change number leads to a spontaneous miscarriage. However, there are also such changes where the pregnancy develops normally, but children with physical and mental problems are born. The following disorders are in that group:
- Down’s syndrome (trisomy 21st chromosome),
- Edward’s syndrome (trisomy 18th chromosome),
- Patau syndrome (trisomy 13th chromosome),
- Klinefelter syndrome (XXY),
- Turner syndrome (X0),
- Change XXX/XYY.
Besides numeric there are also changes in the chromosome structure out of which the most frequent are deletions (a part of the chromosome is missing).
- Wolf’s syndrome – del(4)(p15),
- Cri-du-chat syndrome – del(5)(p15)
Reasons for prenatal diagnostics:
- pregnant women of 35 or older,
- pathologic ultrasound result,
- bad biochemical marker results during the early stage of the pregnancy
- artificial insemination conception,
- family’s congenital disorder history,
- more than two spontaneous miscarriages,
- exposure to some sort of biochemical or biological mutagen radiation
- other high risk factors (marriage between family members, problems during the pregnancy and during the delivery as well as certain diseases of the mother).
Biological material tested in prenatal diagnostics involves:
- Chorionic villus sampling (2 mg of chorionic villus sampling),
- Amniotic fluid (20 ml of amniotic fluid),
- foetal blood (2 ml of foetal blood – heparin),
- peripheral blood lymphocytes,
- tissue (skin),
- abortive material
Gynaecologist decides of the time to take chorionic villus sampling, but they are usually taken in the 10th or 11th week of pregnancy. Amniotic fluid is taken in the 16th or 17th week. Foetal blood is taken in the 21st or 22nd week.
- Results are ready in 8-10 days,
- They are very precise and reliable,
- In order to perform a chromosome analysis of fraternal twins, two amniotic fluids must be taken.