The mortality and birth rates of spina bifida during a period of treatment, selection and antenatal screening in Sheffield, 1963-1978.

The birth rates for all neural tube defects and the mortality rates from spina bifida and encephalocele have been obtained for Sheffield children by examining the congenital anomalies register and death certificates during the period from 1963-1978. The introduction of atenatal alpha foetoprotein screening of all pregnant women in 1977 is associated in time with a sharp fall in the birth rate of neural tube defects. The mortality rate for spina bifida with encephalocele rose gradually from 1967 to 1976, apparently unaffected by the introduction of clinical selection prior to surgery in 1971. The antenatal screening of previously affected families (since 1973) did not affect the mortality rate, but screening the total pregnant population since 1977 has been associated with a sharp reduction in the mortality rate. The mortality rate curve for spina bifida with encephalocele is markedly different from the birth rate curve which makes the common practice of inferring birth rates from mortality rates invalid. There was a gradual increase from 1967 to 1978 in the proportion of children born with spina bifida in any given year who died before their second birthday. This increase appears to have been uninfluenced by the introduction of selection or antenatal screening. The changes in mortality rate and survival may be as much due to unknown factors as to changes in medical management.