Using national perinatal death statistics extending back to the 19th century and more recent and detailed data from Scotland, it can be shown that death rates from central nervous system deformities and from other causes, generally associated with the mother's socio-economic circumstances, are related to the period at which the mother herself was born and reared. For example, the increased death rate from anencephaly which occurred throughout the late 1940s and the 1950s can be attributed to cohorts of women who were all born during the great economic depression of 1926 to 1937. While advances in obstetric care will probably continue to reduce the perinatal mortality rate, it is unlikely that rates similar to those in Sweden can be achieved until a generation of women has been reared in an environment comparable to that in Sweden where social class differences in stature have disappeared.