These tests are SCREENING tests that have been among the routine tests in pregnancy follow-up since 1992. What do these scan? Is there a need to do each one separately?
These tests are a test that calculates the probability of pregnant women carrying the chromosomal diseases known as Trisomy 18 and Trisomy 21, which are relatively more common in all live births. In short, it is not a diagnostic test but a risk determination test. It is made by looking at the mother's blood. These tests give a numerical result that is not open to interpretation. For example, if we talk about the Triple test, values above 1/250 (that is, the probability of being seen once in 250) are considered high risk (or screening positive), values below are considered low risk (or screening negative). It's a very analytical situation. It is not possible for the doctor to comment.
If one of these tests performed on the patient results in a risky area, DIAGNOSTIC TESTS are applied. What needs to be done for this is AMNIOCYNTHESIS (taking a sample from the liquid environment in which the baby is located), CHORIONOUS VILLUS SAMPLING (taking a sample from the baby's partner) or CORDOCYNTHESIS (taking a blood sample from the baby's umbilical cord), depending on the age of pregnancy. These are diagnostic tests. There is also another diagnostic test with 99.9% reliability, called the PRENATAL TEST, which has become popular recently. You can find detailed information about amniocentesis, chorionic villus sampling, cordocentesis and prenatal testing in my other articles.
As can be understood from what I wrote above, even if the result of the screening test performed on a patient is not in the risky area, the risk probability in this regard should not be understood as "0". Let's explain with an example;
Assuming that the screening test result in a patient is 1/225, this means that the child of 1 of 225 patients with the same gestational age and the same values in the blood samples taken carries this chromosomal disease. Since this rate is greater than 1/250, let's do a diagnostic test for this patient.
Assuming that the result obtained in another patient is 1/650, the same risk for this patient means 1 in 650. Since this patient is medically in a lower risk group, there is no need to perform a diagnostic test on this patient. However, the risk is not "0". Similarly, the risk ratio of a patient whose result is 1/2375 is not "0". . It is 1 in 2375.
In short, low risk should not be understood as "0". Although the critical medical rate varies, it has been determined to be 1 in 250 on average.
In summary, your doctor performed these tests on you and the result was in the risk-free zone, but unfortunately you still gave birth to a baby with these chromosomal anomalies. This possibility always exists. If one of these tests has been done, there is no need to do the others. Nowadays, the most preferred one is the double test.
Don't we take similar risk possibilities every moment in our daily lives? For example, the possibility of getting into an accident while driving in traffic. Even if this rate is higher, do people refrain from going to traffic for this reason? It is possible to list thousands of similar examples.
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