Introduction: First trimester screening for Down's syndrome was evaluated by the National Board of Health in 2004, and recommended to all pregnant women in the form of an informed choice. We have reviewed prenatal and postnatal chromosome aberrations in 3 counties in Denmark during the years of implementation in 2004, 2005 and 2006.
Materials and methods: Risk evaluation based on combined screening (fetal nuchal translucency measurement and serum screening of the pregnant woman) was introduced in the counties of Copenhagen, Roskilde and Storstrom, covering approximately 1.1 million inhabitants. We registered the number of chorionic villus biopsies (CVS) and amniocenteses (AC), as well as the number of cases with trisomy, triploidy and sex chromosome aberrations found prenatally. We also registered the number of children born with Down's syndrome during the period.
Results: The number of CVS/AC decreased from 1382 to 790, or 40%. There was an increase in the number of foetuses diagnosed with trisomy 21: in 2004 trisomy 21 was diagnosed in 12 foetuses, in 2006 the number was 30. The number of children born with Down's syndrome was 10 and 5 in 2004 and 2006, respectively. National figures from the Danish central cytogenetic registry confirm a decrease in children born with Down's syndrome.
Conclusion: The implementation of combined screening in 3 counties resulted in a reduction in invasive procedures (chorionic villus samples and amniocenteses) by 40%, which is in accordance with the aims of the National Board of Health. As expected, a significant increase in the number of prenatally diagnosed foetuses with trisomy 21 was observed. The number of children born with Down's syndrome decreased, but the numbers are small. The investigation does not review aspects of organisation or counselling and psychosocial issues.