– What is a double test? What is the purpose of the double screening test?
During the
pregnancy period for
pregnant women, various kinds of tests are done. Double test is also one of these tests.
Double test helps to detect fetal abnormalities. The dual test, also known as the 11-14 week test and double screening test, is a screening test in which the two hormones called PAPP-A and free B-hCG are measured and measured in addition to the fetal nuchal thickness. Double test can determine whether the baby in the mother’s womb is
Down’s syndrome.
Double test results in %85-90 correct, 10-15% error. Gender estimation can not be performed according to the double test result. Gender can not be determined with this test.
– What are the increased risks of birth defects (Down Syndrome)?
– Above 35 years of age pregnants
– Genetic disease problems
– Relative marriages
– Births with previously similar anomalies
– Previous abortion
– Previous child with Down syndrome
– In pregnant women with assisted methods (such as in vitro fertilization and microinjection methods)
The risk of Down’s syndrome is increasing especially in people with Down’s syndrome in older pregnants and particularly high in people with Down syndrome in their family.
To determine the risk of Down syndrome, a double test is performed between 11-14 weeks of gestation and a triple test is performed between 16-18 weeks. Both are “screening tests” that determine of Down’s syndrome and are not definitive diagnostics.
– What is measured in a double test?
Blood analysis applied between 11-14 gestational weeks to the pregnant and free β-HCG and
PAPP-A (pregnancy associated plasma protein) biochemical values are examined.
As its name suggests, PAPP-A is a “pregnancy-specific” protein only found in pregnancy.
Beta HCG is a hormone secreted only in pregnancy. Even when evaluating pregnancy tests, the hormone Beta HCG is measured.
Ultrasound is also used to measure fluid in the nape of the baby. This measure is called the “nape translucency” (NT). In a double screening test is evaluated nuchal translucency measurement combined with biochemical value in the blood. CRL (crown rump lenght) measurements are performed in addition to ultrasound fetal nape thickness (NT) for a dual test.
Biochemical values are changing in Down syndrome …
In the maternal blood of Down syndrome, free β-HCG levels are twice as high as normal while PAPP-A values are 60% lower than normal values.
– The limit for the two tests is 1/250 …
In a “double test”, both biochemical values are assessed in the computer program and a risk ratio appears. If the risk ratio is over 1/250, the test is positive, which means that the patient who is at risk for down syndrome requires advanced examination. The limit value is also called cut off.
Do not worry if the double screening test is positive. Because every 30
pregnant women who tested only one pregnant’s test positive result. In every 23 positive result only one actually carries a baby with down syndrome.
That is, the double test is only a screening test, and even if the test positive your baby is most likely healthy 🙂 In this case, however, it is recommended that the tests that are diagnostic are absolutely necessary.
– What are prenatal diagnostic tests done in
pregnancy?
Diagnostic tests should be performed in cases of double or triple tests are positive. Prenatal tests in pregnancy are chorionic villus biopsy and amniocentesis.
Chorionic villus biopsy is performed between 12-14 weeks. It is based on the principle of chromosome analysis by producing tissue samples taken from placenta of baby.
Amniocentesis is done by producing in the genetic laboratory of the sample taken from amniotic fluid between 16-20 gestational weeks. Both tests result in an average of 2-3 weeks. As a result of the test, the babies’ chromosomes are checked to make sure they have down syndrome.
– What should be done if the double test is positive?
If the double test is positive, the next step is chorionic villus biopsy and obtain a definitive diagnosis by chromosome analysis. In addition, detailed ultrasound examination of the fetus is also recommended.
A second method is amniocentesis at 16 weeks of gestation.
In amniocentesis and chorionic villus biopsy, exact results can be obtained by looking at the chromosomes of the baby. For this reason, both tests are referred to as diagnostic test.
– What should be done if the double test is negative?
The test negative does not indicate that your baby is absolutely healthy, by removing the possibility of down syndrome. For this reason, we recommend you to continue your routine pregnancy follow-up.
The double test also provides information about the NTD (neural tube defects). The AFP value in the triple screening test is important in this regard. Triple test is performed between 16th and 18th gestational weeks of your pregnancy.
“Do they need triple tests of the patients who have had a double test?” The answer to the question varies according to the doctors. Some doctorsthink that this is unnecessary, but some doctors can suggest patients to triple screening tests.
The American Obstetricians and Gynecologists Association recommends direct amniocentesis or chorionic villus biopsy instead of having to perform double and triple tests at over 35 years of age. Because both screening tests ultimately determine the risky group and do not give a definitive result. In addition, after age 35, the risk of Down syndrome and chromosomal anomalies is increasing with age.
An example of a double test:
Interpretation of the double test: When the test report was examined, PAPP-A value: 0.84 MoM was found. The PAPP-A value means that the median value is 0.84 times. In the case of Down syndrome, this value is about 0.40, so the patient is away from the possibility of down syndrome.
On the other hand, the B-HCG value was 0.44 times higher than the median. The median B-HCG level in Down syndrome is 2 MoM. This also removes the person from the point of view of the down syndrome (reduces the probability).
The NT value is also measured like this (1 MoM is normal). If the value is 1.50 Mom, down syndrome probability increases a bit.
The risk of down syndrome and Trisomi 13/18 in < 1/10000
The risk of becoming down syndrome (age risk) only by age is 1:982 (The pregnant is 25 years old)
These values appear automatically in the computer program.
As a result, the patient is NOT in the risky group according to the bilateral test result, the scan is negative.
