There were 3
544 survivors, 1956 SIDS deaths, 2012 SUDI deaths and 11
592 “other” deaths with all variables present. The most prevalent cause of SUDI was “other ill‐defined/unspecified causes” (ICD‐10 code R99) designated as “unexplained” SUDI and comprised 40.4% of all SUDI deaths. “Accidental suffocation in bed” (ICD‐10 code W75) representing 18.7% of the total number of SUDI deaths, comprised the largest proportion of “explained” SUDI (table 1). The most prevalent “other” causes were “congenital malformation of the heart, unspecified” (ICD‐10 code Q249) and “extreme immaturity” (ICD‐10 code P072), representing 4.5% and 4.0% of the total “other” cause deaths, respectively (table 1).
Table 1Most prevalent causes among sudden unexpected deaths in infancy and “other” categories
Table 2Per cent distribution of selected population characteristics by survival status, USA, 2002
The mean birth weight for survivors was 3299 g compared with 2959 g for SIDS victims (p<0.05), 2911 g for SUDI‐unexplained victims (p<0.05), 2994 g for SUDI‐explained and 1919 g (p<0.05) for “other” causes of death. The mean gestational age for survivors was 38.5 weeks compared with 37.6 weeks for SIDS victims (p<0.05); 37.4 weeks for SUDI‐unexplained victims (p<0.05), 37.7 weeks for SUDI‐explained (p<0.05) and 32.7 weeks for “other” causes (p<0.05).
Non‐Hispanic black infants were over‐represented among all causes of death compared with survivors (15.5%). Among SIDS victims, 28.5% were non‐Hispanic black, and among SUDI‐unexplained 32.2%, among SUDI‐explained 34.0% and among “other” causes 25.4% were non‐Hispanic black. Among SIDS and SUDI deaths mothers were more likely to: be born within the USA than among those infants who died of “other” causes; have fewer than 12 years of education; and use tobacco during pregnancy. Also, the infant's sex among SIDS and SUDI deaths was more likely to be male. Multiple births were more frequent among infants dying of all causes compared with survivors and most prevalent among infants dying of “other” causes (13.3%) than among SIDS (5.8%). There was a higher prevalence of maternal diabetes and pregnancy‐induced hypertension among infants dying of “other” causes. Pregnancy weight gain was similar among survivors, and SIDS and SUDI victims, but it was reduced among victims of “other” causes. SGA infants were more prevalent among SIDS (18.8%), SUDI‐unexplained (19.7%), and SUDI‐explained (18.4%) deaths compared with survivors (9.7%). Nevertheless, the prevalence of SUDI‐unexplained infants was highest among infants dying of “other” causes (31.8%, p<0.01). There were fewer LGA infants among all categories of death when compared with survivors. The mean age at death was greatest for SUDI‐explained causes and least for “other” causes.
Logistic regression was used to model the risk for the various causes of death among infants who were small compared with infants who were appropriate for gestational age. The unadjusted odds ratio for SIDS versus survivors among small compared with appropriate for gestational age infants was 2.03 (95% CI 1.82 to 2.27), and for SUDI it was 2.08 (1.87 to 2.32) and for “other” causes 4.19 (4.04 to 4.35). Following adjustment for potentially confounding variables, the adjusted odds ratio for SIDS among small compared with appropriate for gestational age infants was 1.65 (1.47 to 1.85), and for SUDI it was 1.78 (1.59 to 2.00) and for “other” causes 4.68 (4.49 to 4.88) (table 3). LGA infants were at reduced risk for all causes of death (table 3).
Table 3Adjusted odds ratios* (95% CI) for mortality from specified category of death by size at birth
Significant interactions were observed between size and gestational age for SUDI and “other” causes, and between size and tobacco for SUDI and “other” causes. Logistic models were developed to determine the risk of SIDS, SUDI and “other” causes for SGA infants stratified by gestational age (table 4). Compared with infants who were appropriate for gestational age those who were small were at greater risk for SIDS across all gestational age categories. Only the more mature SGA infants (>33 weeks) were at greater risk for SUDI. The least mature SGA infants (24–32 weeks) were at an increased risk for “other” causes (adjusted odds ratio 3.92), but those at >33 weeks were at even greater risk (adjusted odds ratio 5.96 and 5.21 for 33–36 weeks and 37–42 weeks, respectively). In contrast, LGA infants were at reduced risk for all causes of death across all gestational age categories.
Table 4Adjusted odds ratio* (95% CI) for specified mortality category of death stratified by size and gestational age
Logistic models stratified by size and gestational age showed a consistent increased risk for SIDS and SUDI among all sizes of infants of women who smoked compared with non‐smokers in all gestational age categories (table 5). The number of infants born to smokers for infants small and large for gestational age at gestational ages of 24–32 weeks and whose death was categorised SIDS or SUDI was very small and does not provide reliable estimates. There was no increased risk of “other” causes of death among infants who were small or large for gestational age whose mother smoked in any of the gestational age categories except among AGA term infants, where there was a slight increased risk (odds ratio 1.18). For most gestational age and size categories there was at least a trend to a reduced risk of “other” causes of death among smoking mothers.
Table 5Adjusted odds ratios* (95% CI) for specified categories of mortality for infants whose mothers used tobacco and non‐tobacco users stratified by size and gestational age