In this article
- What is the combined test?
- Exams
- What can the combined test reveal?
What is the combined test?
The combined test (or bi-test or duo-test) is a prenatal screening test non-invasive which personalizes the individual risk of giving birth to a child with chromosomal problems (Down syndrome, Edward's syndrome, patau syndrome etc ...), while without providing diagnostic certainties.
When to do it
Normally executable between the eleventh and the end of the thirteenth week of pregnancy, this test is made up of two different exams
- an ultrasound to measure nuchal translucency
- and a maternal blood sample
which lead to the compilation of a report capable of establishing the risk threshold - that is a greater or lesser probability of having a child affected by chromosmic anomalies - calibrated according to the age of the patient.
Read also: The dictionary of pregnancyExams
The combined test requires the mother to undergo two tests that do not require special preparations:
- An ultrasound examination for measure nuchal translucency, ie the measurement of the collection of liquid present in a space between the skin of the nape and the vertebral column of the fetus.
- A blood sample to measure the concentration of two pregnancy-specific substances, the human chorionic beta-gonadotropin (beta-HCG) and plasma protein A associated with pregnancy (PAPP-A).
From 2022 in Del Paese this type of test is free and ticket-free.
What can the combined test reveal?
The data provided by maternal ultrasound and blood tests are processed through predefined algorithms in relation to the mother's age.
The final report obtained does not express a diagnosis, but indicates a risk threshold, i.e. the degree of probability that the fetus is subject to chromosomal abnormalities such as Down syndrome, (trisomy 21), Edwards syndrome (trisomy 18) o Patau syndrome (trisomy 13).
High risk result
A pregnant patient is considered "high risko"if the estimated probability is equal to or greater than a certain threshold which is generally understood between 1: 250 and 1: 385 (the reference risk value for a 35-37 year old woman).
If the risk is lower (eg: 1: 2000) it means that there is less probability than the average of having a child with anomalies, while if the risk is higher (eg: 1: 100) there is a greater risk.
If the risk threshold is too high, it is good practice to continue the investigations with an invasive examination (amniocentesis or CVS) or, if it is decided to avoid invasive tests, with a fetal DNA test.
SOURCE: ISS
Questions and answers
Is the combination test risky?
No, the combined test is non-invasive and does not involve any percentage of risk for the health of the fetus and mother.
When is the combined test done?
The period indicated to undergo the combined test varies from the eleventh to the end of the thirteenth week of pregnancy.
Combined test: what is it for?
It allows to estimate the risk of the fetus having a chromosomal abnormality such as Down syndrome, Edwards syndrome or Patau syndrome.
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- combined test
- test at screening
- dictionary of pregnancy
