UNLABELLED: THE AIMS OF THE STUDY WERE: To evaluate range and median values of NT in a large, unselected Polish population; to determine the value of the 95th percentile and the median values for NT for given weeks of late 1st trimester pregnancy and to determine the level of chromosomal aberration risk corresponding to the values of the 95th percentile in the examined groups; to examine the possible correlation between CRL, NT width as well as the mother's age with the risk of the most frequent chromosomal aberrations.
MATERIAL & METHODS: We have retrospective analyzed 7,866 pregnant women. All fetuses of this women had NT measurement performed, as well as CRL and assessed of the most frequent chromosomal abnormalities. The group of pregnant women was divided into 2 subgroups: until and above 35 years old. All population group was divided into 3 subgroups depending on gestational age (11, 12 and above 13th weeks of gestation).
RESULTS: The median of NT in all population group was 1.5 mm and 95th percentile was 2.4 mm, whilst in group with low risk median of NT and 95th percentile were the same and in group with high risk of chromosomal abnormalities respectively 1.5 mm and 2.5 mm. There were strong correlations between maternal age and the risk of most frequent chromosomal abnormalities from NT.
CONCLUSIONS: The obtained results of median values and the 95th percentiles of NT in the examined group and the age groups under 35 and 35 plus are similar to these quoted by FMF. The risk levels of trisomy of 21st chromosome were similar to the reference values used by FMF. With gestational age, NT value increases in a non-linear way, therefore it is incorrect to use the term "a normal value" for NT, therefore, only the risk level calculated with the dedicated software using NT and CRL measurements with maternal age should be stated.