Infant Mortality: Development of a Proposed Update to the Dollfus Classification of Infant Deaths

Objective

Identifying infant deaths with common underlying causes and potential intervention points is critical to infant mortality surveillance and the development of prevention strategies. We constructed an International Classification of Diseases 10th Revision (ICD-10) parallel to the Dollfus cause-of-death classification scheme first published in 1990, which organized infant deaths by etiology and their amenability to prevention efforts.

Methods

Infant death records for 1996, dual-coded to the ICD Ninth Revision (ICD-9) and ICD-10, were obtained from the CDC public-use multiple-cause-of-death file on comparability between ICD-9 and ICD-10. We used the underlying cause of death to group 27,821 infant deaths into the nine categories of the ICD-9-based update to Dollfus'' original coding scheme, published by Sowards in 1999. Comparability ratios were computed to measure concordance between ICD versions.

Results

The Dollfus classification system updated with ICD-10 codes had limited agreement with the 1999 modified classification system. Although prematurity, congenital malformations, Sudden Infant Death Syndrome, and obstetric conditions were the first through fourth most common causes of infant death under both systems, most comparability ratios were significantly different from one system to the other.

Conclusion

The Dollfus classification system can be adapted for use with ICD-10 codes to create a comprehensive, etiology-based profile of infant deaths. The potential benefits of using Dollfus logic to guide perinatal mortality reduction strategies, particularly to maternal and child health programs and other initiatives focused on improving infant health, warrant further examination of this method''s use in perinatal mortality surveillance.The International Classification of Diseases (ICD), published by the World Health Organization (WHO), serves as the standard for morbidity and mortality classification. Volume two of the ICD 10th revision (ICD-10) provides the structure used to collect, classify, process, and present mortality statistics over time and across geographic regions,^1,2 using a taxonomy that classifies deaths by general disease and affected organ or site. To ensure consistency in the presentation of mortality data across nations, WHO statisticians and medical officers create special tabulation lists with each revision of the ICD. These lists, modified for use in the United States by the Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS), aggregate thousands of single underlying cause-of-death codes into meaningful categories that take into consideration the cause group''s amenability to public health interventions. In the United States, NCHS''s List of 130 Selected Causes of Infant Death is the longstanding method for aggregating cause codes for infant mortality surveillance.³ One challenge of adapting this list to the statistical study of infant mortality is that contiguous code blocks do not necessarily reflect common etiologies.^4–6Alternative classification schemes for infant mortality have been proposed to improve the utility of the ICD underlying cause-of-death code groups for targeted public health efforts. Isolation of prematurity-related deaths, for example, has been a particular challenge for infant mortality surveillance.^6–9 To more accurately reflect deaths caused directly or indirectly by prematurity, NCHS has begun tracking preterm-related mortality using selected cause codes originally identified through a clinical and literature review of 20 leading causes of infant death.^5,10,11 Although this measure is specific to the impact of prematurity on infant mortality, by combining conditions from different sections of the ICD into one with a common set of health determinants, it is an example of the kind of causal grouping critical to health assessment and prevention efforts.The Dollfus classification system, published in 1990 by researchers from the University of North Carolina at Chapel Hill and the North Carolina Center for Health Statistics, aggregates infant deaths based on common etiology and their amenability to prevention strategies⁴ into eight mutually exclusive groups: prematurity and related conditions, congenital anomalies, Sudden Infant Death Syndrome (SIDS), obstetric conditions, birth asphyxia, perinatal infections, other infections, and external causes. In 2013, the State Infant Mortality Toolkit, developed through a collaboration among CDC, the Association of Maternal and Child Health Programs, the March of Dimes, and state and national experts in maternal and infant health, emphasized the importance of infant cause-of-death grouping, including Dollfus classification, to assess infant mortality.¹² This toolkit provides an analytical framework that is useful for Collaborative Improvement and Innovation Network (CoIIN) efforts directed toward infant mortality reduction,¹³ Health Resources and Services Administration''s Title V Maternal and Child Health program needs assessment,¹⁴ and other initiatives to improve birth outcomes.¹⁵ The toolkit examined comparability of Dollfus classification using published data aggregated into 130 rankable causes of infant death under ICD Ninth Revision (ICD-9) and ICD-10, cautioning that classification systems are limited by the quality of underlying cause-of-death data. Our method builds upon that earlier work, employing a statistical frequency-based approach applied to individual bridge-coded death records coded under both ICD versions.The most recent update to the original Dollfus classification was published in 1999, when Sowards updated the system to facilitate its use with national data,¹⁶ presenting a modified Dollfus classification built according to cause-of-death coding published in ICD-9. To date, a validated ICD-10 equivalent to the original logic employed by Dollfus et al. has yet to be published. We describe a mapping of Sowards'' 1999 Modified Dollfus Classification Scheme for Causes of Infant Death (hereinafter, 1999 Modified Dollfus Scheme)¹⁷ from ICD-9 to ICD-10 codes.