Background: The Netherlands are lacking reliable national empirical data in relation to the development of birth prevalence of Down syndrome. Our study aims at assessing valid national live birth prevalence rates for the period 1986-2007. Method On the basis of the annual child/adult ratio of Down syndrome diagnoses in five out of the eight Dutch cytogenetic centres, the national annual figures of the National Cytogenetic Network on total numbers of postnatal Down syndrome diagnoses were transformed into national figures on total numbers of postnatal Down syndrome diagnoses in newborn children only. In combination with the national annual data of the Working Group for Prenatal Diagnostics and Therapeutics on numbers of Down syndrome pregnancies not aborted after diagnosis, national figures on birth prevalence were constructed. Results: For the period 1986-2007, results based on the data of the cytogenetic centres are almost similar to the theory-based model data of de Graaf etal., with a small discrepancy of approximately 4%. Down syndrome birth prevalence in the Netherlands shows an upward trend from around 11 per 10000 births in the early 1990s to around 14 per 10000 births nowadays. Conclusion: In spite of expansion of antenatal screening in the Netherlands, Down syndrome live birth prevalence has risen in the last two decades as a result of rising maternal age. This increase in Down syndrome birth prevalence is in contrast to studies from other European countries. © 2011 The Authors. Journal of Intellectual Disability Research

Birth prevalence, Down syndrome, Epidemiology, Theory-based dynamic model,
Journal of Intellectual Disability Research
Erasmus MC: University Medical Center Rotterdam

de Graaf, G, Haveman, M, Hochstenbach, R, Engelen, J.J.M, Gerssen-Schoorl, K, Poddighe, P, … Van Hove, G. (2011). Changes in yearly birth prevalence rates of children with Down syndrome in the period 1986-2007 in the Netherlands. Journal of Intellectual Disability Research, 55(5), 462–473. doi:10.1111/j.1365-2788.2011.01398.x