title: Investigation of area differences in the prevalence at birth of anencephalus in Belfast.
abstract: A retrospective case-control study comparing social and biological factors relating to all stillbirths and liveborn infants with anencephalus (n = 433) and a 10% random sample of all livebirths (n = 107 346) born to women resident in Belfast between 1957 and 1969 was carried out. The aim was to determine whether the large difference in the prevalence rate at birth of anencephalus within this city could be explained by any previously identified risk factors. For the 15 electoral wards the average rate over the study period was lowest in Windsor ward and highest in Court ward--rates 2.7 and 8.0 per 1000 livebirths respectively. Also, for one particular group of women who lived in certain areas of Belfast and who had an abnormal reproductive history the anencephalic rate was between 7.1 and 10.1 per 1000 livebirths depending on their parity. Although reproductive history was significantly associated with the risk of anencephalus this did not explain the area differences in rates within the city. These findings together with other work suggest that there are at least two separate sets of factors influencing the occurrence of anencephalus. One set relates to area of residence and may reflect adverse social circumstances and diet; the second set relates to maternal reproductive history, acts largely independently of the first and may have a genetic basis. Although this hypothesis accounts for a number of observations relating to anencephalus the excess of affected females cannot be adequately explained.
mesh_terms: D000328:Adult; D000757:Anencephaly / Q000453:epidemiology* / Q000209:etiology; D004651:Employment; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008423:Maternal Age; D009660:Northern Ireland; D010298:Parity; D012189:Retrospective Studies; D012923:Social Class