INTRODUCTION: In 2004 the Danish National Board of Health issued new guidelines for prenatal diagnostics in Denmark. The guidelines include a general offer to all pregnant women in Denmark of first trimester risk assessment of combined non-invasive tests integrating measurement of nuchal translucency and maternal biochemistry for detection of fetal chromosomal abnormalities like trisomy 21, and replacing the screening criteria of > or =35 of age.

MATERIALS AND METHODS: The study is based on registered data covering 5,504 pregnancies during the period 1 July 2005 to 31 December 2005 in Aarhus and Viborg Counties.

RESULTS: 77% of the pregnant women had a complete combined test and only 2% declined the program. At a cut off at 1:400 at term the detection rate for trisomy 21 was 85% (CI: 62.1-96.8%) with a false positive rate of 3.4%. There was a significant reduction in the number of prenatal karyotypes from 2002 to 2005 in both counties, with a 58% reduction in Viborg County and 33% in Aarhus County. The percentage of abnormal karyotypes over the same period increased from 2.8%% to 11.4% in Viborg County, and from 7.1% to 15.4% in Aarhus County.

CONCLUSION: With a significant reduction in invasive procedures and a detection rate of 85% with a false positive rate of 3.4%, the results of the first trimester risk assessment program comply with the requirements defined by the Danish National Board of Health.