Down syndrome and maternal age in Japan, 1950-1973.

The mean maternal age and the percentage age distribution of 2,650 mothers of children with Down syndrome were calculated for 1950-1973, from hospital records. Mean maternal age had dropped both for controls (28.55 leads to 27.37) and Down syndrome (31.26 leads to 29.59). The observed maternal age distributions were very similar to those expected in corresponding periods, from the age specific incidences of Collmann & Stoller (1962). It is conceivable that the fall in maternal age in Down syndrome in recent years has resulted from the general trend to decreasing maternal age. There has been no change in the age-specific incidences of Down syndrome. The incidence of Down syndrome seems to be falling in Japan.