The relative risk for standard 21 trisomy has not increased in young mothers in Belgium, 1960–1978

In the present investigation we directly studied the constancy of the relative risks for standard 21 trisomy in Belgium during the period 1960-1978. The relative risk for standard 21 trisomy in different maternal age-groups, as compared to 20-24 years and 40-44 years remained remarkably constant during the period under investigation. The increasing percentage of children with standard 21 trisomy born to younger mothers does not result from an increased risk for mothers of this maternal age-group, but results from the general shift towards a younger maternal age at birth for the total population of births in Belgium.