Prevalence of Down's syndrome in a pregnant population in Finland.

The characteristics of the Finnish parturient have changed in recent years. The mean age of mothers at first delivery is now 29.3 years and the number of women > 35 years of age has increased to 19%. This shift has led to an increase in the prevalence of Down's syndrome. Between 1 January 2002 and 31 December 2006, there were 795 cases of Down's syndrome (27/10,000) in the Finnish Register of Congenital Malformations. The distribution of Down's syndrome in terminated pregnancies and newborns was analyzed in 5-year periods based on maternal age. The distribution of Down's syndrome cases in younger women (< 35 years) and in older women (> or =35 years) at the time of delivery was compared. The majority of new Down's syndrome cases occurred in the group having older women (61.1%), even though 35 years is the arbitrary threshold.