What is tri-test?

What is tri-test and when should it be done? Find out everything you need to know about this prenatal scan.

The tri-test (or triple test) is a set of biochemical tests performed on pregnant women as part of the individual screening for Down's syndrome. It is systematically offered to all pregnant women at the end of the first trimester of pregnancy. We call it the tri-test because it searches and analyzes three substances in the mother's blood : alpha-fetoprotein (also called AFP), unconjugated estriol and chorionic gonadotropin. These are then evaluated with other parameters (the patient's weight, age, whether she is a smoker or not, for example) and compared to the reference values.

How is it made?

The tri-test consists of take a simple blood sample from the pregnant woman, before which fasting is not even necessary. The test is then based on the results of this blood test and those of the first obstetric ultrasound. It will calculate a risk factor for Down's syndrome in the fetus. The amniocentesis, as well as other additional examinations will confirm this result, or on the contrary, demonstrate that there are no abnormalities.

When should we do it?

Typically, the tri-test is performed between the 15th and the 18th week of pregnancy. Since the values ​​examined vary depending on the time of pregnancy, it is often accompanied by a ultrasound.

Analysis of the values ​​of the tri-test

On the basis of the values ​​examined by the tri-test, it is possible to predict and hypothesize about the disturbances the fetus may encounter. If for example, the alpha-fetoprotein decreases between 25 and 30%, we can advance the hypothesis of a trisomy 21. If the alpha-fetoprotein increases, we can assume that there are defects in the neural tube or the abdominal wall. In the latter case, the patient is generally advised to have an ultrasound for further details.

Unconjugated estriol, if it too decreases, can be considered a risk of Down's syndrome. The same is true when the chorionic gonadotropin is about twice as high as normal. If all the values ​​suggest that there is a high risk of Down's syndrome, amniocentesis is recommended, which allows to exclude or confirm the result of the tri-test.

Bi-test and quadruple test: what is it?

There are alternatives to tri-testing. The first being the bi-test (or duo test) performed at the same time as the nuchal translucency (a non-invasive test). The latter, more reliable, is carried out at a stage earlier pregnancy. The quadruple test, for its part, constitutes the tri-test integrated into an assay of inhibin A (a hormone which participates in the regulation of the menstrual cycle). This test is used by pregnant women who, for various reasons, were unable to complete the bi-test or tri-test on time.


by Barbara Ejenguele