Double and triple tests are used to measure the risk of Down syndrome. Researchers are continuing to develop tests with higher success rates. Gynecology and Obstetrics Specialist Op. Dr. Alper Mumcu, En The latest innovation in this regard is the quadruple test, which was recently put forward. Erek He shares what is curious about the test.
What is a quadruple test?
The quadruple test is a screening test that determines the risk of Down's Syndrome, neural tube defect and trisomy 18 in infants, just like the double test and the triple test. Like the other two tests and all screening tests, it does not only determine whether the baby has a disease or not, but only the risk of that disease in that baby. If the risk is above acceptable limits, further and diagnostic examinations should be carried out in these expectant mothers.
What is a quadruple test?
The quaternary test is based on the determination of the levels of four different substances in the blood sample from the expectant mother. The levels of these substances are processed by computer programs considering the variables such as age, smoking, weight and height at the expected birth date of the mother and a risk is determined as a result.
The items examined in the quadruple test are:
- Alpha-feto protein (AFP)
- Estriol (E3)
- Dimeric inhibin-A (DIA)
Human chorionic gonadotropin (hCG) is the basic hormone of pregnancy. It starts to rise in the early stages of pregnancy 14-16. gradually decreases after reaching the maximum value between weeks
Alpha feto protein is a protease secreted from the baby's liver. From the baby to amniotic fluid and then the blood passes to the mother. During the course of pregnancy, the blood level of the expectant mother shows a slow but steady increase.
Estriol, on the other hand, is a kind of estrogen hormone secreted from the placenta, which is also a baby's tissue.
All of these substances were examined in the triple test.
In the quaternary test, another substance called dimeric inhibin-A was added.
What is dimeric inhibin-A?
Inhibin is a hormone produced in ovaries in women and in testes in men. It affects the secretion of FSH in the brain and plays a role in ovulation and sperm production. There are 2 types of inhibin-inhibin-A and inhibin-B. In men, only inhibin-B is produced, while females have both inhibin-A and inhibin-B production.
In addition, inhibin-A is produced in the placenta in pregnant women and is added to the bloodstream of the expectant mother.
The inhibin-A level in the blood of pregnant women increases gradually during the first 10 weeks and then remains stable until about 25 weeks. When the last trimester is entered, it starts to rise again and reaches its highest level at term.
Studies have shown that blood inhibin-A levels are higher if Down syndrome is present in the baby. Because of this elevation, it is thought that inhibin-A levels can be used as screening test for Down syndrome. However, when evaluated alone, inhibin-A can recognize only 41% of Down Syndrome cases. For this reason, they were evaluated together with different substances and the highest sensitivity was obtained when evaluated together with the other three items.
It is extremely important whether DIA and other substances are affected by some maternal characteristics. It was found that maternal age did not affect DIA levels, whereas body pain was inversely proportional. Similarly, hCG levels differ between different races. AFP levels are also affected in patients with insulin-dependent diabetes.
When is the quadruple test performed?
Although DIA levels are relatively constant in the second trimester of pregnancy, other parameters change. Therefore the ideal time for quadruple testing is 16-18 of pregnancy. are the week.
What is a positive test?
In the quadruple test, a positive test is mentioned if the risk for Down syndrome, neural tube defect or Trisomy 18 exceeds the accepted normal limit. A positive test does not indicate a definite disease in the baby, while a negative test does not guarantee a healthy and healthy baby.
What should be done in the presence of a positive test?
There are a number of alternative ways in which a screening test, the quadruple test, is positive, ie the risk is high. This is the most preferred method in the presence of a positive test.
The second option is to examine the ultrasound findings that may be related to the condition that leads to a positive test and to decide on amniocentesis in the light of these findings. This method should be used only when the risk is at the limit or the expectant mother does not favor the amniocentesis.
How reliable is the quadruple test?
The reliability of the quadruple test is suggested to be higher than the triple test. In the largest study of this issue published in The Lancet in March 2003, nearly 50,000 women underwent quaternary tests and were found to be 81% successful. In another study conducted on 2300 women, a success rate of 85% was reported.
Since the quadruple test is a very new test, more studies are needed to make it widely available and to calculate its reliability more realistically.