Pregnancy is the most sensitive and important period of a woman's life. That's why expectant mothers spend almost every day during the 9-month period thinking about the baby and the baby's health. During this period, week by week nutrition, exercise, doctor's checks and many other issues are important. Especially during pregnancy, many tests are performed that concern the general health of the baby and make it possible to follow the developmental stages. One of these tests is the double screening test. In the dual screening test, which has been implemented both all over the world and in our country since 2000, some chromosomal anomalies that may be present in the baby during pregnancy are investigated. According to the results of this test performed in the first trimester (the first 3 months of pregnancy), the risk of chromosomal anomalies called trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome) in the baby is investigated. These diseases generally refer to diseases with mental retardation and some organ anomalies. This is actually why these tests are called intelligence tests among the public. However, the truth of the matter is that the double test is not a test that measures the baby's intelligence level or how smart he is.
When and how is the double screening test done?
The double test, in which some chromosomal anomalies in the baby are measured, is performed by taking blood from the expectant mother. For this, blood is taken from the mother between 11-14 weeks of pregnancy. This process is just like normal blood tests. There is nothing to worry or worry about. In the double screening test, β-hCG and PAPP-A levels are measured in the expectant mother's blood. This measurement result is formulated with the mother's age and some other characteristics, and the result of the test is determined with the help of a computer.
Dual combined test
The baby's nape is added to the formula of the dual screening test. If the thickness (NT) is also added, the accuracy of the result is higher. The screening test in which nuchal translucency is also added is called a combined test (double combined test). The double combined test is a test performed by combining the double test with the baby's nuchal translucency. The dual combined test is a more detailed and sensitive test than the classical dual test. Because with the double screening test, down se While approximately 65% of babies with syndrome can be detected, this rate can increase to 85% with double combined testing. However, it is important to underline that; Neither test can detect with complete certainty the risk that the baby may have Down syndrome. Because, for some part of the pregnancy of expectant mothers carrying a baby with Down syndrome, the results of these tests will not be high risk and will be normal.
Is the result of the double screening test definitive?
Dual test While the value obtained as a result represents a maximum accuracy of 65%, this value is 85% in the double combined test. In this regard, it cannot be said that the tests definitely show whether these chromosomal anomalies are present in the baby, but only the answer to the question of whether the risk of these anomalies in the baby is higher or lower than normal can be answered.
What if the value of the double screening test is high? What happens?
If the risk of anomaly is higher than normal, CVS (test applied to prove abnormal symptoms seen in the baby between the 9th and 13th weeks of pregnancy) is used to get the answer to the question of whether these anomalies are certain in the baby. ) or amniocentesis (testing the fluid in the baby to detect anomalies in the baby between the 15th and 20th weeks of pregnancy) techniques are applied.
How is the risk determined according to the double test result?
If the value obtained as a result of the double test is within the limit of 1/270, it is decided that there is a high risk for Down Syndrome. When the result of the test is greater than 1/270 (for example, 1/200), the risk of Down Syndrome in the baby is considered higher than normal. According to this result, it cannot be said that the baby definitely has Down Syndrome, the baby may be normal, but there is a risk. In such a case, CVS or amniocentesis must be performed for a definitive diagnosis.
As a result of the double test, the high risk limit for Edwards syndrome (trisomy 18) is accepted as 1/100. When the value obtained is greater than 1/100 (for example, 1/120), the risk of Edwards Syndrome in the baby is higher than normal. There is enough reason to worry, but there is still a chance that the baby may be normal. In this case, CVS or amniocentesis must be performed to make a definitive diagnosis.
However, we underline that this test No matter how high the result is, it does not contain certainty, it only gives information about the existence and magnitude of the risk.
What is nasal bone measurement (nasal bone) and why is it done?
In the double screening test, the presence or risk of chromosomal anomalies called trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome) in the baby is investigated. Another test combined with this dual screening test is the test defined as nasal bone absence in the baby. Because in nasal bone measurement, the presence or absence of nasal bone is evaluated. There are some centers that evaluate the nasal bone, called nasal bone, with ultrasound in combination with a double test. Because the nasal bone, that is, the nasal bone, cannot be seen during ultrasound examination, it increases the risk of trisomy 21 (Down syndrome). Because the nasal bone can be clearly detected by the doctor during ultrasound examination in approximately 98% of normally developing fetuses between 11-14 weeks. However, it cannot be detected in only a small portion of the population, such as 2%. In 70% of fetuses with Trisomy 21, that is, Down Syndrome, the nasal bone cannot be seen. In other words, if the doctor cannot detect the nasal bone during the baby's ultrasound examination, the risk of Down Syndrome in the baby is too high to be underestimated. In the same context, the nasal bone cannot be detected by the doctor in approximately 50% of fetuses with Trisomy 18, that is, Edwards syndrome. Nasal bone is not seen in 30% of fetuses with trisomy 13, which is also a chromosomal anomaly.
Based on all this; It is possible to say that the doctor's ability to detect the noses of the fetuses during ultrasound is important in determining the chromosomal health or normality of the baby. In this regard, nasal bone measurement combined with the dual screening test also provides results that are at least as valid as the dual screening test. However, these tests only give information about whether there is a risk and whether precautions should be taken.
Who has a higher risk of giving birth to a baby with anomaly?
Chromosomal anomaly affects both the baby's physical and mental health. It is the condition of being born mentally deficient or disabled. In fact, this risk, which can be seen in almost all pregnancies, is different for some pregnancies. higher than his men. These are generally;
- Those who are pregnant at ages older than 35,
- Babies of expectant mothers and fathers with genetic diseases,
- Consular marriages,
- Those who have disabilities in other family members,
- Those who have previously given birth to a baby with chromosomal anomalies,
- Those who became pregnant through assisted reproductive methods such as in vitro fertilization and microinjection,
- These can be listed as those who have a history of miscarriage,
- Those who have had a baby die in the womb,
- Those who have a baby with Down Syndrome in their family,
- Those who are malnourished during pregnancy or continue to have harmful habits.
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