Dual Screening Test

Dual Screening Test

The aim of the first trimester screening test, which has been used in the world and in our country since 2000, is to detect Down syndrome at early weeks of pregnancy.

Who has an increased risk of giving birth to a baby with an anomaly (congenital disability)?

Women who became pregnant after the age of 35, those with genetic disease problems, consanguineous marriages, those with a family history of congenital disability, those who previously gave birth to an abnormal (handicapped) baby, those who became pregnant with assisted reproductive methods (such as in vitro fertilization and microinjection methods), miscarriage (abortion) or uterus The risk of giving birth to a baby with anomaly is increased in people who have experienced infant death.

The risk of Down syndrome is also increased, especially in elderly pregnant women and people with a family history of Down syndrome.

11-14 days of pregnancy to determine the risk of Down syndrome. Double test (double test) between weeks 16-18. A triple screening test (triple test) is performed in weeks. Both are "screening tests" that determine the possibility of down syndrome and are not definitive diagnosis.

Dual Screening Test: What to look for?

11-14 days according to the last menstrual period. In the test applied between gestational weeks, blood is taken from the expectant mother and the biochemical values of free β-HCG and PAPP-A are checked.

Free HCG (Free Beta HCG), PAPP-A is the other name of pregnancy associated plasma protein A, that is, “pregnancy-specific plasma protein A” .

As the name suggests, PAPP-A is a "pregnancy-specific" protein found only in pregnancy.

HCG is also a hormone secreted only during pregnancy. Even in the evaluation of pregnancy tests, the hormone HCG is measured.

In addition, ultrasound measurement of the fluid in the baby's neck skin is also made. This measurement is called “nape thickness” (NT). Because nuchal translucency is known as nuchal translucency or nuchal translucency , it is more commonly expressed with the abbreviation "NT" in the medical literature.

In the double test screening, nuchal thickness measurements are combined with the biochemical values in the blood.

For the dual test, CRL (crown rump length, distance between head and rump) measurements are made in addition to the Neck Thickness (NT, nuchal translucency) of the fetus in ultrasound.

Biochemical values change in Down syndrome…

In Down syndrome, free β-HCG values in maternal blood are twice as high as normal , while PAPP-A values are one-2.5, ie 40% of normal .

The limit value in the binary test is 1/250…

In the "double test", both biochemical values are evaluated in the computer program and a risk ratio is revealed. If the risk ratio is above 1/250, the test is positive, that is, the patient in the risk group for Down syndrome requires further examination.

The limit value is also referred to as the threshold or cut off .

If the double screening test is positive, don't worry because one of every 30 pregnant women who have the test is positive. is giving results . Only one out of every 23 pregnant women with a positive result actually carries a baby with Down syndrome.

So, the dual test is just a screening test, and even if the result is high (screening-positive), your baby is very likely healthy. However, in this case, it is strongly recommended to perform diagnostic tests.

What are the diagnostic (diagnostic prenatal) tests performed during pregnancy?

Diagnostic tests should be performed in case of positive double or triple tests that are important for Down syndrome during pregnancy. Diagnostic (prenatal) tests in pregnancy include “chorionic villus biopsy” and amniocentesis.

Chorionic villus biopsy is performed between 12-14 weeks. It is based on the production of tissue samples taken from the baby's placenta and performing chromosome analysis. Amniocentesis is 16-20. It is done by producing the sample taken from the amniotic fluid in which the baby lives between weeks of pregnancy in the genetic laboratory.

On average, both tests take 2-3 weeks to conclude . As a result of the test, it is definitely sure whether the baby has Down syndrome by looking at the chromosomes.

What should be done if the double screening test is positive?

If the test is positive (scan-positive), the next step is to take a small piece from the baby's part of the placenta, called "chorionic villus biopsy", to provide a definitive diagnosis by analyzing it in terms of chromosomes. It is also recommended to carry out a detailed ultrasound examination of the fetus.

A second method is to perform amniocentesis at the 16th week of pregnancy.

In amniocentesis and chorionic villus biopsy, definitive results can be obtained by looking at the baby's chromosomes. For this reason, both tests are referred to as “diagnostic test (diagnostic test)”.

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