Unchanged prevalence of Down syndrome in the Netherlands: results from an 11-year nationwide birth cohort

This study aims to evaluate trends in prevalence of Down syndrome (DS) births in the Netherlands over an 11-year period and how they have been affected by maternal age and introduction of prenatal screening.

Nationwide data of an 11-year birth cohort (1997-2007) from the Netherlands Perinatal Registry were analyzed. First-trimester combined screening was introduced in 2002, free of charge only for women 36 years of age or older and only on patients' request. Changes in maternal age, prevalence of DS births, and rates of births at <24 weeks (legal limit for termination of pregnancy in the Netherlands) during the study period were evaluated using logistic and linear regression analyses.

In total, 1,972,058 births were registered (91% of the births in 1997-2007). Mean prevalence of DS was 14.57 per 10,000 births (95% confidence interval 14.43; 14.73); 85% of DS were live births. No significant trend in overall prevalence of DS births was observed (p = 0.385), in spite of a significant increase of mean maternal age during the same period (p < 0.001). The increased prevalence of DS births at ≥ 24 weeks among women ≥ 36 years of age (p = 0.011) was offset by a significant increase in the proportion of DS births at <24 weeks among women aged <36 years (p = 0.013).

The proportion of DS births in the Netherlands has not changed during the period 1997-2007.