Incidence of congenital malformations in the regions of England and Wales.

Abstract

Slight attention was paid to the epidemiology of congenital malformations before the discovery that exposure of the mother to infection by rubella during early pregnancy could affect the development of the fetus (Gregg, 1941; Swan, Moore, Mayo and Black, 1943). Most malformations had been looked upon as inevitable happenings due to faults of development which were outside the scope of preventive medicine. Increasing use of X rays during pregnancy and studies of background radiation then suggested that these might be concerned in initiating malforma tions, and in 1959 a study was published associating their incidence in parts of New York State with natural radiation from the ground (Gentry, Park hurst and Bulin, 1959). Subsequent work has not, however, so far established the existence of any significant association with background radiation arising from either soil or water supply. In 1968 Laurence, Carter and David reported a thorough investigation of the possible factors which might be concerned in the incidence of 835 cases of congenital malformation of the central nervous system discovered among births occurring during 1956-62 in the mining valleys of Glamorgan and Monmouth and the Vale of Glamorgan. Local variations in the incidence rates of such malforma tions were compared with geological features, water supplies, rainfall, sunshine, background radiation, radioactive fall-out and population density but none of these factors seemed to account for the differences. The only pregnancy factor with evident significance was an increased incidence of influenza. The incidence rate per 1,000 live and stillbirths found in this South Wales survey for anencephaly, spina bifida and hydrocephalus malformations was 8-1, similar to that found in Liverpool (7-4) by Smithells (1962) and in Belfast (8-3) by Stevenson and Warnock (1959). Lower incidence rates had been found in population surveys elsewhere. A nation-wide survey of perinatal mortality resulting from 7,117 singleton births and com prising deaths in the first four weeks of life and stillbirths, which occurred in Great Britain in March to May 1958, was carried out by the National Birthday Trust (Butler and Bonham, 1963). This yielded some 500 congenital malformations of all kinds, but the total was insufficient for assessment of significant differences in incidence in the separate regions. By the registration of causes of stillbirth based on certification according to the International List it becomes possible to bring together for each sex in 1963-66 the prenatal deaths from each kind of neural tube malformation (rubrics Y 38-0 anencephaly, Y 38-1 hydrocephalus, Y 38*2 spina bifida), with all other congenital malformations (Y 38*3?Y 38-7) and postnatal deaths from corresponding causes at ages under 1 year and at 1-4 years in categories 750-752 and 753-759. In 1963-66 there were 24,458 stillbirths and deaths at 0-1 year assigned to these numbers arising from three and a half million live and stillbirths in all, and the various rates for each sex have been calculated in the present paper for each Hospital Region in the hope that geogra phical variations will provide some clue to the causes of malformations, particularly those of the neural tube. The total incidence of malformations in infants is not fully revealed by the deaths classified to them as underlying cause, since some affected children die of concomitant causes and others continue to live with the disability, but within England and Wales, where the rules and procedure of certification are tolerably constant, one can assume that regional rates compounded of prenatal and postnatal deaths are comparable with each other though lower than total incidence rates derived from surveys. In the final section of the paper the various regional distributions are compared with those for mortality of females from cardiovascular diseases, and other conditions for which there are indications of a 'water factor' apparently related to hardness of local water supplies (Morris, Crawford and Heady, 1961; Crawford, Gardner and Morris, 1968). 67