Anencephalus in the Oxford Record Linkage Study area.

The incidence of anencephalus in the largely rural areas of Oxfordshire and west Berkshire from 1965 to 1972 was ascertained from the files of the Oxford Record Linkage Study as 1-49 per 1000 total births. There was little variation within the area, but there was a marked increase in incidence over the eight years of the study. There was a slight seasonal variation, with an excess of conceptions in the first two quarters of the year, a slight excess of births to primiparous women and to women aged between 20 and 24 years. There was an increase in incidence with falling social class, with a significant excess of fathers who were printers, painters and decorators, transport drivers or in the armed forces. Among 115 siblings, 11 (9-6 per cent) had defects of the central nervous system, and the incidence of anencephalus among twins was twice as high as expected.