All About Prenatal Cell-Free DNA Screening
Share This Article
Learn about donation options.
Subscribe our newsletter
to be notified when we publish
Nowadays, it is no longer a luxury for expectant parents to consider whether their offspring will be a girl or a boy during pregnancy. The priority is, of course, to give birth to a healthy individual. At this stage, the analysis and screening tests performed during pregnancy gain serious importance. Fetal DNA Test is also a screening and diagnostic method that gives essential information about the baby’s health in the womb.
What is a Fetal DNA Test?
The screening tests performed to understand whether the baby has specific chromosomal abnormalities while still in the mother’s womb is called the Fetal DNA Test. The application of the Fetal DNA Test is based on the principle of taking samples from the structures of the baby’s cells and examining the DNA fragments in these samples. In this way, it is checked whether there are certain genetic disorders in the baby.
Why is the Fetal DNA Test Done?
Ultrasound scans during pregnancy can only give information about the health problems that the baby can show physically. It does not give much information about the genetic defects that are congenital and do not show with their external appearance. On the other hand, the Fetal DNA Test is a method applied to detect some chromosomal anomalies in a developing baby in the womb.
Genetic diagnostic tests are not applied in every pregnancy. However, in risky pregnancies, it is applied with the advice of a doctor and the mother’s consent. Experts consider the following situations risky. Being 35 years of age or older for the mother-to-be creates a risk situation. As age progresses, the likelihood of genetic disorders in the baby increases.
Absence of nasal bone, hyperechogenic focus (White-bright spot) in the heart or kidney, nuchal translucency measurement values in the risky range, and ultrasonographic findings suggesting chromosomal anomalies such as a curved little finger.
It is a severe risk situation for the expectant mother to have a history of trisomy in her previous pregnancies or the parents themselves.
Presence of genetic abnormalities in close relatives but not in the parents themselves.
Undesirable positive findings in some tests performed in the second and second trimesters.
If families have one or more of these risks, the obstetrician may want to perform any of the genetic screening tests.
Genetic Screening Tests
The screening methods that allow the genetic examination of the baby in the mother’s womb are as follows.
Free Fetal DNA Test (Nifty Test)
The baby’s DNA fragments (free fetal cells) begin to mix with the mother’s blood from the first weeks of pregnancy. The Free Fetal DNA Test is the screening test using free fetal cells in a blood sample taken from women who are expecting a baby. As the weeks progress, the amount of DNA mixed into the mother’s blood increases. For the test to work correctly, the rate of free fetal DNA in the mother’s blood is expected to be above 4%.
Although this method is never a definitive diagnostic test for a chromosomal anomaly, it is a method with high accuracy. If you ask how Free Fetal DNA Test is done; It is reliable; it does not endanger the baby’s life; it is only examined with a blood sample taken from the mother through a vein.
It can detect Down Syndrome with a sensitivity of over 99%. In case of high-risk test results, amniocentesis or chorionic villus biopsy, which are definitive diagnostic tests, may be requested. Sometimes the results are ambiguous. In this case, patients should receive genetic counseling, detailed ultrasound, and other diagnostic tests should be performed. If there is a problem with these, amniocentesis or chorionic villus biopsy may be requested.
This test is quite costly. However, it is precious as it gives information about whether the fetus has genetic disorders such as Trisomy 13, Trisomy 18, Trisomy 21 with its results.
The cells that make up the fluid in the placenta and the baby’s cells have the same genetic structure. The baby’s DNA is also examined by examining the sample taken from the baby’s environment, namely the amniotic fluid. Amniocentesis is also a diagnostic test applied with this principle.
Amniocentesis is applied in pregnancies that give risky results in a double, quad, or detailed ultrasound scan tests. It can be applied after 14-16 weeks of pregnancy. It allows detailed examination of all chromosomes and gives precise results in genetic anomalies. However, the most significant disadvantage of the procedure is that it may bring risks such as bleeding, water leakage, and even pregnancy loss.
Chorionic Villus Biopsy (CVS)
It is a screening test applied by taking a piece from the baby’s partner and examining it. The baby is expected to be in the appropriate position, accompanied by an ultrasound device. The desired tissue is reached with a needle by passing through the abdominal layer, and the uterine wall and the sample piece are taken.
In cases where a definitive diagnosis is desired, it can be made starting from the 11th week. However, if the doctor deems it risky, he may request a Chorionic Villus Biopsy even at the 9th week. This process, which takes 15-20 minutes, is not painful, but it can be a little uncomfortable in terms of how it is applied. After the procedure, the expectant mother may experience drip bleeding or periodic contractions. In case of an increase in bleeding or the severity of contractions, a doctor should be consulted immediately.
It is a test performed by taking blood from the baby’s umbilical cord or any suitable vein. It is applied after the 20th week of pregnancy. It should not be forgotten that there are risky situations such as bleeding, water leakage, and pregnancy loss in cordocentesis as in amniocentesis.
Most Common Anomalies As A Result Of Fetal Genetic Screening Tests
Trisomy 13 (Patau Syndrome):
It has 3 of the 13th chromosomes in the baby instead of 2. It has a probability of 1 in 10000 live births. It can cause problems in the baby’s vital organs such as the brain and heart and cause facial defects. These babies usually do not live very long.
Trisomy 18 (Edward Syndrome):
Having an extra chromosome 18 in the baby is the condition. It can manifest as growth deficiency, digestive and respiratory system disorders, mental retardation, head and face deformity.
Trisomy 21 (Down Syndrome):
It is the condition of having one extra chromosome 21. In addition to noticeable physical differences such as short stature, short neck, blunt fingers, flat face, slanted eyes, it causes advanced mental retardation.
The only wish of every expectant parent is to give birth to a healthy baby. For this reason, from the moment the pregnancy is learned, blood tests and ultrasound scans are performed immediately, and the baby’s development is followed regularly every month. During this detailed follow-up, some results may raise severe suspicions that the baby has chromosomal disorders.
In risky situations, you may need to have one of the Fetal DNA Test applications to get more precise information about the baby’s health in the mother’s womb. In this process, you must get detailed information from your specialist doctor about which method you will apply, the risks and cost of applying, and then decide to apply the method.
We are supporting women all around the world before, during, and after their pregnancy by providing up-to-date information and advice, and tools.
We kindly ask for your support to continue to produce content for you and to enable you.