29Background: Sudden unexpected death in infancy (SUDI) comprises both natural and 30 unnatural causes of death. However, a few epidemiological surveys have investigated 31 SUDI in Japan.
32Objective: This retrospective study was conducted to investigate the recent trends of 33 circumstances and risk factors of sleep-related SUDI cases. 34 Methods: Forensic pathology sections from eight universities participated in the 35 selection of subjects from 2013 to 2018. Data obtained from the checklist form were 36 analyzed based on information at postmortem.37Results: There were 259 SUDI cases consisting of 145 male infants and 114 female 38 infants with a mean birth weight of 2888 ± 553 and 2750 ± 370 g, respectively. Deaths 39 most frequently occurred among infants at 1 month of age (18%). According to 40 population-based analyses, the odds ratio (95% confidence interval) of mother's age 41 ≤19 years was 11.1 (6.9-17.7) compared with ages 30-39. The odds ratio for the fourth-42 and later born infants was 5.2 (3.4-7.9) compared with the frequency of first-born 43 infants. The most frequent time of day for discovery was between 7 and 8 o'clock.
44Co-sleeping was recorded for 61%, and the prone position was found for 40% of cases 45 at discovery. Mother's smoking habit exhibited an adds ratio of 4.5 (2.9-5.8).
46Conclusion: This study confirmed the trends that have been observed for sudden infant 47 death syndrome; particularly, very high odds ratios were evident for teenage mothers 48 and later birth order in comparison with those in other developed countries. The child of 49 a young mother tended to die within 2 months of age. To our knowledge, this is the first 50 report of an extensive survey of sleep-related SUDI in Japan. 3 52 97 Postmortem examinations included histology, toxicology, biochemistry, virology, 98 and bacteriology. [19,20] Tests for assessing inherited metabolic disorders were 99 conducted nationwide in the routine examination for newborns. [21] Genetic testing for 5 100 arrhythmic disorders was also conducted for cases examined in this study. [22] Data 101 used for analysis consisted of DSI information, therapeutic information in emergency 102 care, and maternity passbook. The checklist form, consisting of 41 items, was filled in 103 initially by each center. Then the lists were transferred to one site to confirm unclear 104 issues and aggregate the data. 105 The forensic pathology sections of the following eight universities participated in 106 this study: 110 University School of Medicine. The areas of these facilities cover six prefectures in 111 which approximately 14% of the entire population resides, and this percentage was 112 applied to calculate the annual rate per 1000. Every sudden infant death had been 113autopsied, but there could have been some deaths that had not received autopsy outside 114 major centers in Japan, whose exact number remained unknown. Although DSI was 115 performed by the police for all cases, not all items were optimal, particularly, for the 116 sleep environment such...