Non-invasive method in pregnancy; Free Fetal DNA
Chromosome Test in the Maternal Blood
CFF DNA test; It is based on the detection of DNA cells belonging to the fetus in maternal blood. Although it cannot be defined as a diagnostic test, it is considered as a highly significant screening test. It would be appropriate to name it as chromosome analysis with free fetal DNA.
Fetal DNA is in small particles outside the cell. DNA cells of the fetus originate from the disrupted placental cells and are constantly released into the mother’s blood. In less than 2 hours, the half-life of these cells expires and they begin to disappear. They disappear from the blood of the mother in a short time after birth. In addition to the woman’s own DNA, the mother woman has 2-4% of fetal DNA.
Determination of fetal DNA in the womb can be preferred in the following situations:
* Advanced maternal age,
* Detection of screening positivity in screening tests including double, quad test and integrated test,
* There is a numerical chromosome anomaly in the mother or father candidate,
* Translocation carriage in terms of chromosome disease in mothers or fathers,
* Family history of chromosome anomaly,
* It is the determination of chromosome anomaly marker in ultrasonography.
Invasive methods such as amniocentesis can give an idea about the numerical anomalies of chromosomes without the possibility of fetal loss and other complications.
The accuracy of the test is at least 99%.
It can be applied from the 11th week of pregnancy.
In the application of the test, the patient should be informed by a knowledgeable and experienced specialist physician or geneticist. Then 20 ml of peripheral venous blood is drawn from the mother into a special blood collection tube. Blood taken with special storage and shipping conditions is delivered to the LifeCodexx laboratory (abroad). First, plasma of blood and then genetic material is separated from plasma. After this procedure, a very small amount of genetic material is obtained and this material is referred to as fetal fraction. A genomic information is generated and reproduced for analysis. Final evaluation is completed with special software. Here, the amount of genetic material of 21, 18 and 13 chromosomes, sex chromosome anomalies including numerical anomalies related to X and Y chromosomes and a limited number of single gene diseases are determined. Trisomy 21 is the most common chromosomal anomaly in live births. If this amount of genetic material cannot be determined, the test will say ‘no results’ and blood will need to be drawn from the mother again. If the amount of genetic material is sufficient, this data; It is compared with the normal value ranges in cases with diploid normal chromosome set. Whether they exceed them or not is calculated with a statistical value called ‘Z Score’. The result is given within 15 days.
When the result is reported as ‘normal’, it means that there is no need for additional invasive testing other than screening tests and ultrasonography. Indicates that there is no possibility of numerical anomaly for chromosome 13, 18 and 21. If it is reported as “abnormal”, invasive tests should be discussed with the patient. Obtaining an abnormal result indicates that the baby has high trisomy disease. However, it cannot show how much the problem affects the baby or how severe the disease is. Nondisjunction, mosaic or translocation, which are subtypes of trisomies, can only be determined by a detailed chromosome analysis, for which sufficient genetic material must be obtained by invasive testing.
With this test, it is not possible to evaluate the structural diseases in chromosomes. Only numerical evaluation can be made. In addition, if there is an incompatibility between the fetus and the placenta and the result is positive, the placenta may have been affected, but the fetus may have been unaffected. Diagnosis will also be insufficient in Mosaic Down syndrome. In these cases, it is not possible to replace the invasive test.
In multiple pregnancies, it cannot be determined which fetus belongs to the genetic material obtained from the mother’s blood, and when there is a high risk, both fetuses are genetically examined.