LETTERS
Validity of Data for Anencephalus To the Editor The paper by Trimble and Baird (‘78) on the incidence of central nervous system defects in B.C. raises questions about the accuracy of some of the figures used to discuss the epidemiology of these congenital anomalies (Elwood, ‘76). Trimble and Baird (’76) compared the recorded prevalence at birth of CNS malformations in the B.C. Health Surveillance Registry (formerly Registry for Handicapped Children and Adults) with data prepared by the federally co-ordinated Congenital Anomaly Surveillance System. They indicated that the B.C. Registry reported 92 cases of anencephalus and the Congenital Anomaly Surveillance System only 79 for the years 1966-1969. The correct total of infants with anencephalus from our records for those years is 82, not 79. The remaining deficit is accounted for by incomplete results in 1966 and 1967, the first two years of the pilot study, when six stillbirth and death records were not received. Other infants were described as “monster,” an inexact diagnosis, and could not be definitely
counted as anencephalics. Since that time, our data are believed to reflect virtually complete ascertainment. It would seem that reasonably accurate counts of anencephalus may be obtained both from vital statistics documents and registries. It is important to note, however, that the vital statistics documents must be adequately screened and include all conditions listed on the death and stillbirth registration forms, not just the “cause” of death or stillbirth. LITERATURE CITED
Elwood,J. Mark 1976 Anencephalus and Spina Bifida in North America. In: Birth Defects, Risks and Consequences. Sally Kelly, Ernest B. Hook, Dwight T. Janerich and Ian H. Porter, eds. Academic Press. New York, pp. 3-19. Trimble, B. K., and P. A. Baird 1978 Congenital anomalies of the central nervous system incidence in British Columbia, 1952-1972. Teratology, 17: 43-50. PHILIP BANISTER Health Protection Branch, Department of National Health and Welfare, Ottawa, Ontario, Canada, K I A OL2
Use of Mortality Data to Ascertain Anencephalus To the Editor Trimble and Baird (Teratology 1978, 17: 43-50) studied central nervous system anomalies reported by the British Columbia Health Surveillance Registry and concluded that “multiple sources of ascertainment and follow-up of children beyond one year of birth are necessary for adequate reporting even for these sorts of defects which have generally been thought to be readily recognised at or shortly after birth.” We do not believe that such extensive efforts are required to document the prevalence at birth of anencephalus, although they are justifiable for other defects. TERATOLOGY (1979) 00: 269-272.
Table 3 in their paper shows that from 19661969 there were 92 cases of anencephalus reported to the registry, compared to 79 cases reported by the Congenital Anomaly Surveillance System and published by Elwood (‘76); thus the provincial registry, using multiple sources of ascertainment, reported 14%more cases than the simpler system dependent on vital records and birth notifications. However, other published data (Elwood, ’74) shows that for these years the use of death and stillbirth records alone ascertained through Statistics Canada, yielded 90 cases of anencephalus.
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LETTERS TABLE 1
Recorded cases of anencephalus in British Columbia, 1964-1970 Reastry (Trimble and Baird)
Special study (McBride)
Vital records (Statistics Canada)
23 20 22 27 19 22 24 157 90
25 22 23 27 19 21 24 161 90
26 21 23 20 18 21 24 161 90
Year: 1964 1965 1966 1967 1968 1969 1970 Total 1964-1970 Total 1966-1969
’
’ Based on a recheck of Reastry material; 92 cases shown in Trimble and Baird (‘78) by error. 2Based on data supplied in 1972 and used in Elwood (‘74). Recent recheck by Banister yields 92 cases. To provide a better comparison between the British Columbia registry and routine death and stillbirth notifications we have compared the numbers of anencephalics recorded in British Columbia from 1964 to 1970 by (a) the B.C. registry - data supplied by Doctor Baird, (b) a special study of anencephalus and spina bifida in B.C., based on this registry but using slightly different coding practices (McBride, ’79), and (c) routine death and stillbirth notifications, supplied by Statistics Canada to Doctor Elwood in 1972. These data (table 1) show the excellent agreement between routine death notifications and more complex systems for ascertainment of anencephalus; agreement which would be expected for a totally fatal and easily diagnosed condition. The lower number of cases recorded by the Surveillance System reflects the usual difficulties of a new recording system: 1966 was the first year studied (see accompanying letter from Doctor Banister). We do not wish to detract from the importance of having the best possible registries for congenital abnormalities, or from Trimble and Baird’s excellent DaDer, - - . and we believe that
death registrations are an inadequate method of ascertainment for any other major defect. However, for anencephalus, the study of stillbirth and death notifications provides a very valuable and efficient method of studying prevalence rates a t birth for a condition which displays intriguing geographical, secular, seasonal, ethnic and other variations. LITERATURE CITED Elwood, J. M. 1974 Anencephalus in Canada 1943-1970. American Journal of Epidemiology, 100: 288. 1976 Anencephalus and spina bifida in North America. In: Birth Defects Risks and Consequences, S. Kelly, E. B. Hook, D. T. Janerich and I. H. Porter, eds. Academic Press, Inc., New York, pp. 3-19. McBride, M. L. 1979 Sib risks of anencephaly and spina bifida in British Columbia. American Journal of Medical Genetics, in press. J. MARK ELWOOD Department of Health Care and Epidemiology, University of British Columbia, Vancouver, Canada V6T 1 W5
M. L. MCBRIDE Health Surveillance Registry, Division of Vital Statistics of British Columbia, Vancouuer, Canada V6J 4M3
Letter to the Editor I agree with Doctors Banister and Elwood that reasonably accurate counts of anencephalus may be Obtained, both from vita1 statistics documents and registries, and I do not
think we are a t issue here. I would like to quote from the paper “of all of the congenital malformations, those of the CNS are among the most readily recognized at or
Validity of Data for Anencephalus To the Editor The paper by Trimble and Baird (‘78) on the incidence of central nervous system defects in B.C. raises questions about the accuracy of some of the figures used to discuss the epidemiology of these congenital anomalies (Elwood, ‘76). Trimble and Baird (’76) compared the recorded prevalence at birth of CNS malformations in the B.C. Health Surveillance Registry (formerly Registry for Handicapped Children and Adults) with data prepared by the federally co-ordinated Congenital Anomaly Surveillance System. They indicated that the B.C. Registry reported 92 cases of anencephalus and the Congenital Anomaly Surveillance System only 79 for the years 1966-1969. The correct total of infants with anencephalus from our records for those years is 82, not 79. The remaining deficit is accounted for by incomplete results in 1966 and 1967, the first two years of the pilot study, when six stillbirth and death records were not received. Other infants were described as “monster,” an inexact diagnosis, and could not be definitely
counted as anencephalics. Since that time, our data are believed to reflect virtually complete ascertainment. It would seem that reasonably accurate counts of anencephalus may be obtained both from vital statistics documents and registries. It is important to note, however, that the vital statistics documents must be adequately screened and include all conditions listed on the death and stillbirth registration forms, not just the “cause” of death or stillbirth. LITERATURE CITED
Elwood,J. Mark 1976 Anencephalus and Spina Bifida in North America. In: Birth Defects, Risks and Consequences. Sally Kelly, Ernest B. Hook, Dwight T. Janerich and Ian H. Porter, eds. Academic Press. New York, pp. 3-19. Trimble, B. K., and P. A. Baird 1978 Congenital anomalies of the central nervous system incidence in British Columbia, 1952-1972. Teratology, 17: 43-50. PHILIP BANISTER Health Protection Branch, Department of National Health and Welfare, Ottawa, Ontario, Canada, K I A OL2
Use of Mortality Data to Ascertain Anencephalus To the Editor Trimble and Baird (Teratology 1978, 17: 43-50) studied central nervous system anomalies reported by the British Columbia Health Surveillance Registry and concluded that “multiple sources of ascertainment and follow-up of children beyond one year of birth are necessary for adequate reporting even for these sorts of defects which have generally been thought to be readily recognised at or shortly after birth.” We do not believe that such extensive efforts are required to document the prevalence at birth of anencephalus, although they are justifiable for other defects. TERATOLOGY (1979) 00: 269-272.
Table 3 in their paper shows that from 19661969 there were 92 cases of anencephalus reported to the registry, compared to 79 cases reported by the Congenital Anomaly Surveillance System and published by Elwood (‘76); thus the provincial registry, using multiple sources of ascertainment, reported 14%more cases than the simpler system dependent on vital records and birth notifications. However, other published data (Elwood, ’74) shows that for these years the use of death and stillbirth records alone ascertained through Statistics Canada, yielded 90 cases of anencephalus.
269
270
LETTERS TABLE 1
Recorded cases of anencephalus in British Columbia, 1964-1970 Reastry (Trimble and Baird)
Special study (McBride)
Vital records (Statistics Canada)
23 20 22 27 19 22 24 157 90
25 22 23 27 19 21 24 161 90
26 21 23 20 18 21 24 161 90
Year: 1964 1965 1966 1967 1968 1969 1970 Total 1964-1970 Total 1966-1969
’
’ Based on a recheck of Reastry material; 92 cases shown in Trimble and Baird (‘78) by error. 2Based on data supplied in 1972 and used in Elwood (‘74). Recent recheck by Banister yields 92 cases. To provide a better comparison between the British Columbia registry and routine death and stillbirth notifications we have compared the numbers of anencephalics recorded in British Columbia from 1964 to 1970 by (a) the B.C. registry - data supplied by Doctor Baird, (b) a special study of anencephalus and spina bifida in B.C., based on this registry but using slightly different coding practices (McBride, ’79), and (c) routine death and stillbirth notifications, supplied by Statistics Canada to Doctor Elwood in 1972. These data (table 1) show the excellent agreement between routine death notifications and more complex systems for ascertainment of anencephalus; agreement which would be expected for a totally fatal and easily diagnosed condition. The lower number of cases recorded by the Surveillance System reflects the usual difficulties of a new recording system: 1966 was the first year studied (see accompanying letter from Doctor Banister). We do not wish to detract from the importance of having the best possible registries for congenital abnormalities, or from Trimble and Baird’s excellent DaDer, - - . and we believe that
death registrations are an inadequate method of ascertainment for any other major defect. However, for anencephalus, the study of stillbirth and death notifications provides a very valuable and efficient method of studying prevalence rates a t birth for a condition which displays intriguing geographical, secular, seasonal, ethnic and other variations. LITERATURE CITED Elwood, J. M. 1974 Anencephalus in Canada 1943-1970. American Journal of Epidemiology, 100: 288. 1976 Anencephalus and spina bifida in North America. In: Birth Defects Risks and Consequences, S. Kelly, E. B. Hook, D. T. Janerich and I. H. Porter, eds. Academic Press, Inc., New York, pp. 3-19. McBride, M. L. 1979 Sib risks of anencephaly and spina bifida in British Columbia. American Journal of Medical Genetics, in press. J. MARK ELWOOD Department of Health Care and Epidemiology, University of British Columbia, Vancouver, Canada V6T 1 W5
M. L. MCBRIDE Health Surveillance Registry, Division of Vital Statistics of British Columbia, Vancouuer, Canada V6J 4M3
Letter to the Editor I agree with Doctors Banister and Elwood that reasonably accurate counts of anencephalus may be Obtained, both from vita1 statistics documents and registries, and I do not
think we are a t issue here. I would like to quote from the paper “of all of the congenital malformations, those of the CNS are among the most readily recognized at or
