Dear Expectant Mother and Father,
Down syndrome is characterized by the increase in the number of chromosomes, which is normally 46 in humans, to 47 as a result of the addition of an extra chromosome number 21, and is characterized by various levels of mental retardation in the newborn baby. In addition, it is a disease that causes abnormalities at different rates in the heart, gastrointestinal system, urinary system and central nervous system.
Although the risk of developing this disease increases in mothers over the age of 35 who have a family history of Down Syndrome, according to studies. It is observed that babies with the syndrome are mostly born at a young age and from mothers who do not have any genetic disease in their family. For this reason, even if the mother has no risk factors, some tests are applied to expectant mothers to screen for the disease.
For this purpose, a Perinatal Examination is performed at 11-14 weeks;
-PAPP-A and Free-Beta HCG hormones or fetal-DNA.
-Measurement of the baby's nuchal skin transparency with ultrasound
strong> .-Presence of nasal bone, facial angle
-Heart rate, ductus venosus and tricuspid valve examination with Doppler
-Examination is performed for some organ-specific markers.
PAPP-A and Free-Beta HCG hormones 9-13 It is checked by taking maternal blood during the pregnancy weeks. 3-4 ml of blood is taken from the forearm vein with a sterile syringe. It is a method that takes about a minute and is harmless to the mother and baby. Redness may occur only at the site where blood is taken. Within a few hours, this area of redness will heal. It would be more preferable if the blood test section is performed at the 10th week.
In babies with Down Syndrome, the 11-14th week of pregnancy. Between weeks, there is a fluid collection at the nape of the neck, and this fluid disappears after the 14th week. Nose skin transparency measurement is a completely harmless examination that can be performed by an experienced physician during a normal pregnancy ultrasound.
Again, with the help of ultrasonography, it can be performed between 11-14 weeks. Between weeks, it is checked whether the baby's nasal bone can be seen. In babies with Down Syndrome, the ossification of the nasal bone is delayed and thus ultrasound The nasal bone cannot be seen. In addition, facial angle measurement is also done for this purpose. Cardiovascular and valve blood flow measurements mentioned above are taken with Doppler. The examination is performed for the appearance and findings of all organs specific to this week. Thus, when performed together with ultrasound and blood tests, it detects Down Syndrome with a probability of around 93-97%.
In addition to these tests, if the 11-14 week examination time is missed or not performed, it detects Down Syndrome at 16-20 weeks. During the gestational weeks, a triple screening test based on checking the mother's blood for AFP, HCG and Estriol (when inhibin is added to this trio, it is called a quadruple test) is performed. The probability of this test alone detecting Down Syndrome is 64%. The benefit of performing both the 11-14 week screening test and the triple test in the same expectant mother has not been demonstrated yet and may cause confusion.
In addition to the blood tests mentioned above, blood taken from the mother, which has been in practice since the last few years, has not yet been demonstrated. A screening test is also performed with the fetal DNA test. Although this test has higher sensitivity, it is an expensive test. Although fetal-DNA testing is a preferred method, it may not be essential as it is not covered by social insurance and is not cheap. There are two options here: Either the fetal-DNA test, although expensive, can be performed as a first stage test (starting from the 10th week). Or, in the first stage, if the other blood test, PAPP-A and beta-hCG test, and ultrasonography examination are in the 11-14 week range or the gestational week is 15-20 weeks, then the triple-quadruple test is performed and if the risk ratio obtained is not satisfactory, then In this case, fetal DNA testing can be done as a second step or CVS / amniocentesis test, which is a direct diagnostic test, can be done. If you need details on this subject, please consult your doctor.
All of these tests are screening tests and mathematically calculate the possible risk in the current pregnancy. In other words, it determines what the risk is. Determining whether the baby's chromosome is normal or not can only be done through genetic examination of fetal cells. It can be detected by me. To this end; CVS (chorion villus sampling) at 11-14 weeks or 15-20 weeks. Amniocentesis is performed in the following week.
Chorion villus sampling is based on the principle of taking a cell sample from the baby's placenta (partner) by entering the mother's womb with a needle under ultrasound guidance. The advantage of this procedure is that it gives early results (1-2 weeks) and can be applied early, thus allowing early diagnosis of an abnormal baby. The disadvantage is that sometimes the test must be repeated in 0.5-1% of cases. After chorionic villus sampling, there is a two in a thousand (0.2%) chance of miscarriage or premature birth.
Amniocentesis is taking a sample of the baby's fluid by entering the mother's womb with a needle under ultrasound guidance. The advantage of this procedure is that the need to repeat the test is very low (0.1%), and the disadvantage is that it gives results later (3 weeks) and can be applied in later weeks of pregnancy, thus the pregnancy grows until the time of intervention. Tissues taken after CVS and amniocentesis are subjected to various processes in the genetic laboratory and these cells are multiplied in appropriate environments to obtain results. Rarely, failure may occur during the proliferation of these cells due to reasons such as insufficient tissue taken, bloody amniotic fluid, or infection of the culture medium. This may lead to no results from genetic research. However, this probability is very low. After amniocentesis, there is a possibility of miscarriage or premature birth with a probability of two in a thousand (0.2%).
As a result of the examination, it is useful to know that other tests may need to be performed for a definitive result and that the baby may miscarry or be born prematurely, although with a low probability, during these tests. . It should be noted that, even though it is very unlikely, these tests may not yield results due to unforeseen problems that may arise from the procedure or the laboratory environment.
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