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First trimester screening (combined test)

During the 1990s, an association between the thickness of the nuchal translucency (NT) and the risk of chromosomal aberrations (trisomy 21 – Down syndrome, trisomy 18– Edwards syndrome and trisomy 13 – Patau syndrome) was detected.

To put it very simply, the risk of chromosomal aberrations rises sharply at NT values greater than 2.3 mm. The examination requires a high level of training and experience of the doctor performing it and favourable conditions to achieve a high-quality ultrasound image of the embryo. The combined test consists of biochemical screening from blood (beta free subunits of HCG and PAPP-A) at week 11 and first-trimester ultrasound screening (NT examination and the presence of the nasal bone (NB)) at week 13.

First-trimester screening (combined test) detects 85 to 90% of affected foetuses. Therefore, a negative outcome of the first trimester screening does not fully exclude aneuploidies (Down, Edwards and Patau syndrome) in the foetus. It only indicates substantially reduced risk of aneuplodia in the foetus.

In case of a positive outcome of the screening, the patient is referred to a genetics specialist who may recommend additional examinations (cfDNA, CVS, AMC) to exclude foetal defects.

To improve the results, it is possible to add the so-called triple test in the second trimester of pregnancy (week 16). The sensitivity of this examination is only 50-60%, but if combined with the screening results from the first trimester, this so-called integrated screening has an accuracy of up to 98%. A positive outcome of the integrated screening indicates the increased probability of foetal Down syndrome and it is recommended to undergo a genetic consultation or other examination methods to rule out this disease.

The maximum accuracy of the screening examination can be achieved thanks to the utilised state-of-the-art instruments and the evaluation by a specialist with the FMF certificate, an institution with international competence which precisely determines the conditions under which screening can be performed.