Comparisons of secular and seasonal variations in the incidence of anencephalus in Belfast and four Scottish cities, 1956-66.

Abstract

Epidemiological investigations in the United Kingdom have shown that the secular and seasonal variations in the incidence of anencephalus in Belfast (Elwood, 1970) resemble those in Scotland (Record, 1961; Leck and Record, 1966). In both areas a small but definite increase in frequency and a signifi cant excess of anencephalic births in winter compared with summer have occurred in recent years, this secular trend differing from the decline reported in Birmingham, England, by Leck (1966). Outside the United Kingdom a marked decline in incidence has been observed in New York State (Gittelsohn and Milham, 1962) and in Boston (Naggan, 1969), the latter city also exhibiting an excess of anencephalic births in summer. Owing to the large geographical area of Scotland we have compared the secular trends and variations by season in Belfast with those in four major Scottish cities, namely Aberdeen, Dundee, Edinburgh, and Glasgow, observed over the period 1956-66. In addition, we examined, using multivariate analysis, the associations between the monthly number of anencephalic births and certain meteorological com ponents of season based on data from Belfast, Glasgow, and Edinburgh. Because no convincing explanation has yet been offered for the apparent significant seasonal variation in the monthly incidence of anencephalic births, we tested the hypothesis that the monthly number of cases was independent of air temperature, rainfall, and sun shine occurring at certain times during the gesta tional period of these pregnancies. The specific hypothesis and analytical methods adopted are detailed later.