Prenatal Diagnostics During the First Trimester in the Clinical Praxis

Overview

Background.
Biochemical screening test for Down’s syndrome now offered in the 16th to 20th week of pregnancy reaches 60–65 % sensitivity with 5 % false positives. Newly introduced combined test done between 11+0 to 13+6 weeks of pregnancy, maternal serum biochemistry (free beta hCG a PAPP-A) and foetal nuchal translucency measurement, offer very early identification of Down’s syndrome in foeti. The purpose of our study was the introduction of the new method and confirmation of the expected sensitivity and false positivity in our conditions. 

Methods and Results.
The combined test identified 5 of 6 (83 %) of Down’s syndrome foeti from the studied group of 2573 pregnancies. The false positive rate was 2.2 %. Women aged 35 years or more represented 15% of our cohort. One Down’s syndrome foetus with normal combined test was identified in the 21 week of pregnancy due to its heart failure which was diagnosed with ultrasound. Morover, 4 foeti with Edwards- and one with Turner syndrome were identified. 

Conclusions.
In comparison with the second trimester biochemical screening, the first trimester combined test offers the information at the end of first trimester, it has higher sensitivity and low false positivity. The combined test gives clear outcomes, easy audit and control over ultrasound and biochemical results. Introduction of the first trimester screening requires strict adherence to the method both by the sonographer and the biochemical laboratory, and the acceptance of rigorous audit rules. 

Key words:
first trimester screening, prenatal diagnosis, biochemical screening.