Analyses – Invasive – Genetics
This analysis is done between 16th and 24th week of pregnancy with an ultrasound. During this procedure 10 – 20 ml of amniotic fluid that surrounds the baby is taken. The baby’s cells float in the amniotic fluid and they are tested in this analysis.
This amount can be compensated in a few hours. Most women do not consider that this method is painful and describe the experience as giving a blood sample.
Amniocentesis is indicated in cases in which the risk of birth of a child with a chromosomal disorder is greater than the risk of the method itself. The latest studies dealing with the risk associated with this procedure, state that the risk is 0.1% (published in: R. Akolekar, J. Beta, G. Picciarelli, Ogilvie C. And F. D’Antonio, Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis, Ultrasound Obstet Gynecol 2015; 45: 16-26).
When a pregnant woman is over 35, in addition to determining the biochemical and ultrasound markers in the first trimester, it is necessary to do the amniocentesis because of increased risk of chromosomal disorders.
After the intervention the patient is advised to rest for the next 24 hours, in some cases tocolytic therapy is given as a precautionary measure, however, hospitalization is recommended in case of twin pregnancy and uterine contractions.
If the woman is Rh negative, and before the intervention Rh antibodies have not been found in the blood, the patient is given a protective injection with antibodies immediately after the amniocentesis.
Analysis of amniotic fluid can go in two directions:
1. The traditional method
- Amniotic fluid cells are cultivated in a medium
- The analysis of the karyotype can detect changes in the number and structure of all 46 chromosomes
- Amniocentesis is done in the period between 16th and 24th week of pregnancy
- It is necessary to have 20 ml of amniotic fluid in a sterile syringe at room temperature
- The sample is delivered within 12 to 15 hours from the time of sampling
- This result is obtained in 8 to 10 days
This method gives a complete karyotype.
- This method can also detect only specific numerical changes – on the 13th, 18th, 21st and the sex chromosomes X and Y in the sample taken from the amniotic fluid,
- The sample can be taken in the period between the sixteenth and twenty seventh week of pregnancy
- 5 ml of amniotic fluid is necessary for this test
- The result is obtained in 24 hours
- The sample does not have to submitted on the same day
The disadvantage of this method is that it cannot detect structural alterations in the chromosomes, as well as numerical changes in chromosomes other than those listed.
Chorionic villus sampling (Chorionic Villi Sampling – CVS) is based on the fact that the chorionic tissue’s genetic and chromosomal properties are identical with fetal’s genetic and chromosomal properties. The gynaecologist decides when the sample of chorionic villi is taken, but it is usually in the period between 10th and 13th week of pregnancy for the purpose of karyotyping, determining metabolic disorders, DNA analysis of gene loci and fetal infection.
Chorionic villus sampling includes taking a small sample of the placenta – fine needle passes through the abdominal wall of the mother, then through the uterine wall in order reach the tissue of the placenta.
This procedure is carried out under ultrasound control.
According to the data of the latest studies dealing with the risk associated with this procedure, the risk rate is 0.2% (published in: R. Akolekar, J. Beta, G. Picciarelli, Ogilvie C. And F. D’antonio, Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis, Ultrasound Obstet Gynecol 2015; 45: 16-26).
The most common indication is advanced maternal age, because it is known that women older than 35 are more likely to have children with Down syndrome. This diagnostic method is also recommended if in history of pregnancy, there is evidence that the previous child had chromosomal abnormalities or the parents have genetic anomalies.
Prenatal diagnosis of chorionic villus can go in two directions:
1. Traditional method
Chorionic villi – Traditional method
- Chorionic villi cells are cultured in the medium.
- Karyotype analysis can detect changes in the number and structure of all 46 chromosomes.
- The sample is be delivered within 12 to 15 hours from the moment of sampling.
- The result is obtained in 8 to 10 days.
This method gives a complete karyotype.
Chorionic villi – QF-PCR
- This analysis can only determine certain numerical abnormalities (chromosomes 13, 18, 21, X and Y) in the sample.
- This result is obtained in 24 hours.
- This method is used to test certain mutation or if the family history has certain issues.
- The sample does not have to be delivered on the same day.
A limitation of this method is the inability to detect structural changes in chromosomes, or numerical changes in chromosomes other than those listed.
Cordocentesis is done if for some reason you are late for amniocentesis or you did not get the adequate results from the previous analyses (screening tests, ultrasound, and amniocentesis).
It is done after the 20th week of pregnancy.
Cordocentesis is an invasive intervention of sampling fetal blood from the umbilical cord. 1 -3 ml of fetal blood with heparin is taken. It is usually done for specific reasons so as to determine the karyotype of the baby, check the presence of certain infections or abnormalities.
Cordocentesis detects chromosomal defects and fetal anemia.
It detects infections such as toxoplasma (which may lead to miscarriages) and measles, as well as loss of vision or hearing, brain injury, hydrocephalus, epilepsy.
This procedure is similar to amniocentesis procedure. The doctor monitors the inside of the placenta with an ultrasound and introduces a needle through the umbilical cord. Then s/he takes a certain amount of blood sufficient for analysis and creation of karyogram from the corresponding blood vessel. Also, if the woman is Rh-negative, and prior to the intervention Rh antibodies have not been found in the blood, immediately after the cordocentesis the patient is given a protective injection of antibodies.
1. The results are obtained in 5 – 7 days.
2. They are very precise and reliable.
3. In order to perform chromosomal analysis of fraternal twins, two fetal blood samples must be taken.
Peripheral blood karyotype
Karyotype from peripheral blood lymphocytes is to be done in couples with infertility problems or frequent spontaneous abortions in the first trimester of pregnancy.
- It is necessary to take 5 ml of peripheral blood with heparin.
- The result is obtained in 5 – 7 days.
- The sample is delivered within 12 to 15 hours from the moment of sampling.
Abortive material karyotype
The karyotype of abortive material is worth doing because a large number of pregnancies end in miscarriage at an early stage.
The most common genetic abnormality are as follows:
Autosomal trisomy 52%
Age of women is one of the risk factors for spontaneous abortions.
20 to 30 years old 9 – 17%.
35 years old 20%.
40 years old 40%.
45 years old 80%.
- The result is obtained in 8 – 10 days.
- The abortive material sample must be delivered within 12 to 15 hours from the time of the intervention, in saline solution, in a sterile container (preferably in a sterile urine container).
Chromosomal Aberrations Analysis
Testing chromosomal aberrations refers to biological dosimetry based on the detection of specific chromosomal rearrangements (dicentric and ring chromosomes accompanied by acentric fragments), which may be formed only under the influence of the radioactive (ionizing) radiation (α, β, γ, x, x-ray), which has the necessary energy to create such a damage.
This test creates the conditions in cells in which genetic disorders appear in the form of specific morphological structures, primarily micronuclei (separated parts of the core which are formed from chromosomal fragments), and depending on their number, the total exposure may be estimated.
Micronucleus test is a sensitive indicator of chromosomal damages and is being widely used to determine the presence and extent of chromosomal damage in people exposed to genotoxic agents in their workplace and living environment