Anencephalus: a changing sex ratio.

The sex ratio of infants born with certain congenital abnormalities diverges widely from unity. There is evidence that these sex ratios vary from place to place and in different races (Gittlesohn and Milham, 1962; Emanuel, 1972). Stocks (1970) has shown that within 25 countries of largely European stock there is a close positive correlation between the divergence of the sex ratio of congenital abnormalities of the central nervous system from unity and the infant mortality of these conditions, and also between the sex ratio of combined infant deaths and stillbirths from these conditions and their perinatal loss rates in the Hospital Regions of England and Wales. Czeizel, Vizkelety, and Szentpeteri (1972) have pointed out a similar relationship between the prevalence of congenital dislocation of the hip and the sex ratio of affected infants. Few studies have been made of secular changes in the sex ratio of congenital abnormalities. The significant variations in the sex ratio of infant deaths from various congenital abnormalities in England and Wales reported by Rogers and Morris (1971) present problems in interpretation because of difficulties in classification and lack of data concerning stillbirths and surviving infants. The secular variations in the sex ratio of anencephalus in Belfast reported by Elwood (1970) are based on 221 cases occurring over six years, and with a study on this scale significant results are not to be expected, nor are they claimed. The present study of the sex ratio of anencephalus in the United Kingdom has been undertaken in the hope that it might give some insight into the nature of these relationships.