Risk assessment of trisomy 21 by maternal age and fetal nuchal translucency thickness in 7,096 unselected pregnancies in Slovenia

Abstract

Aim: To evaluate the screening for trisomy 21 by maternal age and nuchal translucency in a low-risk population.

Methods: Screening was performed in 7,096 singleton pregnancies. The estimated risk for trisomy 21, the detection rate (DR), false positive rate (FPR) and the cut-off nuchal translucency thickness to obtain a 5% FPR were calculated.

Results: The median maternal age was 28.6 years. The estimated risk for trisomy 21 was 1 in 300 or greater in 2.4% (171 of 7,096) of all pregnancies and in 75% (9 of 12) of trisomy 21 pregnancies. The DR for all aneuploidies was 83.3%, and 75% for trisomy 21. The estimated FPR at risk 1 in 300 for the whole population in 2004 was 3.8%. It is predicted to remain below 4% at least until 2007; to achieve a 5% FPR in 2007 the risk limit 1 in 400 is proposed.

Conclusions: Screening for trisomy 21 in a low-risk population in Slovenia gives comparable results to those in other countries. The only result that varies is the percentage of screen positive patients at the risk limit 1 in 300. We believe the risk limit should be specifically estimated for each country based on its population distribution of maternal age.