The clinical usefulness of biochemical (free β-hCg, PaPP-a) and ultrasound (nuchal translucency) parameters in prenatal screening of trisomy 21 in the first trimester of pregnancy

Abstract

Objectives: The aim of the study was to analyze the correlation of multiples of the normal median of PAPP-A, free β-hCG levels and nuchal translucency values in prenatal, first trimester screening of trisomy 21 in pregnant women.

Material and methods: 251 pregnant women underwent antenatal screening at 11-13+6 weeks of pregnancy which was composed of the measurement of free β-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein (PAPP-A) levels in the maternal serum and an ultrasound assessment of nuchal translucency (NT). The pregnant women with a high risk of trisomy 21 (≥ 1:300) were given amniocentesis to verify fetal defects. There were 217 cases of normal fetal karyotype and 34 cases of trisomy 21. PAPP-A, β-hCGMoM and NT values were analyzed for the predefined ranges.

Results: 85% cases of trisomy 21 had elevated free β-hCGMoM (> 1.5) and only 53% of these had a PAPP-AMoM result below 0.5 (p < 0.05). Analysis of NT in selected ranges of β-hCG (> 1.5) and PAPP-AMoM (< 0.05), which are typical for Down Syndrome values, showed that not all fetuses with Down Syndrome presented with an increased NT. Respectively 44.15% and 26.5% of fetuses presented with increased NT. Characteristic for trisomy 21, a correlation with all 1st trimester screening tests' parameters occurred in only 23.5% of cases. In 53% of cases the results were atypical.

Conclusions: The PAPP-A and β-hCG values in the selected MoM ranges did not shown a correlation to the NT measurement, therefore they are independent factors in the diagnosis of trisomy 21. Simultaneous biochemical and ultrasound testing is an indispensable condition for prenatal diagnosis of trisomy 21 in the 1st trimester of pregnancy.

Keywords: PAPP-A; free β-hCG; nuchal translucency (NT); prenatal screening; trisomy 21.