Down syndrome and maternal age in Japan, 1950–1973

The mean maternal ageand the percentage agedistribution of 2,650 mothers of children with Down syndromewere calculated for 1950–1973, from hospital records. Mean maternal agehas dropped both for controls (28.5527.37) and Down syndrome(31.2629.59). The observed maternal agedistributions were very similar to those expected in corresponding periods, from the agespecific incidences of Collmann & Stoller (1962). It is conceivable that the fall in maternal agein Down syndromein 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 syndromeseems to be falling in Japan.