[Increase in the incidence and risk of birth of children with Down's syndrome in Leningrad (1982-1989)].

Among 559,286 infants born in Leningrad in 1982-1989, there was revealed 744 infants (1.33/1000) with Down's syndrome (DS). The age distribution for their mothers as well as for 79,571 parturient women in the general population was investigated. The data regarding the period studied was compared with the results of a similar investigation conducted during of 1945-1961. A decrease in maternal age in the population was demonstrated. This was more pronounced for the mothers of affected infants. A 1.4- to 2.2-fold increase of birth risks for DS was found in all maternal age groups. The doubling of the risk value occurred by the age of 30-34, in contrast to 35-39 in 1945-1961.