Tritest: what it is and when it should be done

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Philippe Gloaguen
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Tritest

Il tritest is a prenatal screening test that consists of the measurement of three markers: alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol.



I results blood tests can help make a type assessment probabilistic the risk of the fetus having a birth defect, such as Down syndrome or neural tube malformations. But let's see when it should be done and how the tritest.



In this article

  • What is it
  • When should it be done
  • Reading the results
  • Screening tests
  • Difference between bitest and tritest

What does the Tritest consist of

It is a non-invasive procedure that is performed through a blood test - with little or no risk to the mother or the child's development - with which they are analyzed three values:



  • AFP: alpha-fetoprotein is a protein produced by the fetus. Elevated levels of this protein may be indicative of neural tube defects or non-closure of the fetus's abdomen.
  • hCG: human chorionic gonadotropin that is the hormone produced inside the placenta. Low levels of this hormone can indicate potential problems with pregnancy, including miscarriage or ectopic pregnancy.
  • Estriol: Estriol is an estrogen produced by both the fetus and the placenta. Low estriol levels can indicate the risk of having a baby with Down syndrome, especially when coupled with low levels of AFP and high levels of HGC.

Abnormal levels of these markers may indicate the presence of:

  • neural tube defects, such as spina bifida and anencephaly
  • multiple pregnancies
  • an incorrect dating of the pregnancy, which is therefore more advanced or further behind than is believed
  • Down syndrome: the fetus has an extra copy of chromosome 21. It can cause health problems and, in some cases, learning difficulties
  • Edwards syndrome: it can cause very serious complications, in many cases fatal.

Tritest and Down syndrome

The tritest also evaluates the probability that the fetus is affected by Trisomy 21, that is Down syndrome, but also by Edwards syndrome.



The risk is considered high when the result is greater than 2,5 MoM.

When should the tritest be done?

The tritest is more reliable and accurate when performed between the 16th and 18th week of pregnancy, but can also be carried out earlier, the 15° and 22° week of pregnancy.

In the new LEA (Essential levels of assistance) the Tri Test for AFP, total or fractional free HCG, has been included as a service offered to pregnant women. If the woman shows up for the first meeting at a time that does not allow the offer of the first trimester test, a test such as the triple test must be offered at a later time.

Read also: Screening test and diagnostic test

What happens if the test gives an abnormal result?

In the event that i test results are suspicious or abnormal, the gynecologist may require further investigation with a more invasive examination but this time of a diagnostic type, such as amniocentesis. We remember, in fact, that the tritest is only an exam that offers a result probabilistic: this means that it does not guarantee a real diagnosis of anomaly in the fetus, but only a calculation of the percentage of risk that the child has problems or birth defects.

On the contrary, amniocentesis will analyze the amniotic fluid taken in the laboratory and will be able to diagnose the presence of various diseases. Even a structural (morphological) ultrasound will be able to complete the diagnostic picture by checking the age of the fetus, the skeletal system, the spinal cord, the kidneys, the heart, the brain.

Screening test

Screening tests don't just look at blood test results - they compare a number of different factors (including maternal age, diabetes and other mother's conditions, and blood test results) to estimate the likelihood that the unborn child has an anomaly. These tests, therefore, they do not diagnose a problem: They can only indicate that further tests are required.

Difference between tritest and bitest

As we have seen, the tritest is a non-invasive test that is performed on maternal blood between the 16th and 17th week of pregnancy. The test analyzes three substances (alpha-fetoprotein, beta HCG and estriol) and provides a personalized statistical result.

Il bitest it is also a non-invasive test that is carried out on maternal blood between the 11th and 13th week of pregnancy. It is associated with nuchal translucency and analyzes measures the concentration of free b-hCG (chorionic gonadotropin) and PAPP-A (the pregnancy-associated protein) levels in maternal blood.

References

  • American Pregnancy
  • Triple-marker test as screening for Down syndrome: a meta-analysis
  • Ministry of Health

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