Assessment of Prevalence of Persons with Down Syndrome: A Theory-based Demographic Model

Abstract

Background The Netherlands are lacking reliable empirical data in relation to the development of birth and population prevalence of Down syndrome. For the UK and Ireland there are more historical empirical data available. A theory-based model is developed for predicting Down syndrome prevalence in the Netherlands from the 1950s onwards. It is likewise applied to Ireland and the UK for the purpose of validation. Furthermore, a prediction to 2050 is constructed. Materials and Methods Maternal age births data in the general population, maternal age related risk of Down syndrome, data on selective terminations of Down syndrome pregnancies and mortality rates (from 35 studies from the 1930s until today) were obtained to create this model. Results For the Netherlands, nowadays birth prevalence is estimated at 14 per 10 000 with around 275 total annual births. The impact of selective abortion is lower than in the UK. Present Dutch Down syndrome population prevalence is estimated, according to this theorybased model, at 7.7 per 10 000 and the grand total at 12 600 individuals. The prevalence of 'older' persons with Down syndrome (over 40 years of age) in the Netherlands will reach a peak in 2010, a doubling compared to 1990, implying an increased demand on medical care and counselling. Validity of this theory-based model was examined by comparison with relevant available empirical data from the three countries. The model shows a good fit with historical empirical research, notably four UK and two Irish population prevalence studies and eight birth prevalence studies. Conclusions A theory-based model for Down syndrome prevalence provides supplementary data in situations with a lack of empirical material and can be used for understanding and predicting long-term developments.

The population prevalence of Down’s syndrome in England and Wales in 2011

“…The estimated life expectancy for people with Down's syndrome born in 2011 was greater than that estimated by other studies; 11,13,14 a median life expectancy of 58 years compared with 57 years in Baird and Sadnovnick 11 and 50 years in De Graaf et al 13 The improvement of median life expectancy is mainly due to the improved infant survival after birth.…”

“…De Graaf et al 13 have estimated the population prevalence of people with Down's syndrome as 0.61 per 1000 persons, with an estimated total of 34 160 persons with Down's syndrome in England and Wales. The difference in prevalence can mainly be explained by different estimates of survival rate.…”

“…This was assumed to apply regardless of the year of birth. This method of estimating the survival rates at 1, 5 and 10 years was developed by de Graaf et al 13 Population prevalence of Down's syndrome in 2011…”

Estimation of the number of people with Down syndrome in the United States

“…5 No population-based registry exists for people with DS in the United States, although the need has been highlighted at national conferences. 6,7 In a recent study, de Graaf et al 8 used and validated an alternative approach for the United Kingdom, the Netherlands, and Ireland. In estimating population prevalence, the model uses maternal-age birth data in the general population, maternal age-related chances for a live birth with DS, data regarding elective terminations, and DS-specific mortality rates.…”

“…For this age group, Shin et al 11 estimated a population prevalence of 10. 8,13 For the period 1909-2007, the number of births of children with DS was estimated based on counts of births by maternal age. Presson et al 13 adjusted for the effect of elective pregnancy terminations by assuming a constant rate of 13% reduction in live births with DS from 1980 to 2007.…”