The incidence of anencephalus and other malformations of the central nervous system (CNS) is much higher in the United Kingdom than in other countries of Western Europe which were not industrialized to the same extent. In the UK the incidence is highest in the unskilled manual occupational group, especially in the large cities of the North of England, Scotland and Northern Ireland. Standards of living have been low in these areas for many years and deteriorated sharply at the time of the worldwide industrial depression from 1928 to 1934. The population tended to be stunted in stature and to show other signs of chronic malnutrition.

The cohort of women born in these years had an unusually high stillbirth rate from anencephalus (and from all other CNS malformations) from about 1946 onwards. It was highest in the early 1960s when these women were at the peak of their reproductive activity. This suggests that the severe malnutrition to which they were subjected before and soon after birth resulted in severe damage, which reduced their reproductive efficiency as demonstrated by the unusually high perinatal death rate from all CNS malformations. Not surprisingly the death rate rose sooner, lasted longer and reached a higher level in social classes IV and V than in social classes I and II. Other evidence of damage was an increase in the incidence of low birth weight babies with a corresponding increase in the perinatal death rate from this cause.

In Scotland the stillbirth rate from anencephalus was approximately 2·1 per 1000 in 1948–49, 3·4 at its highest point between 1961 and 1963 and 2·1 in 1968, by which time the women born in the years of the depression had completed their childbearing. A teratogen acting during a particular period of time could not provide a satisfactory explanation for this sequence of events.