Sex Differences in Mortality Among Infants with Trauma: A Nationwide Registry-Study in Japan, 2004-2023

Despite evidence of sex-related survival differences in postpubertal trauma populations, whether biological sex influences mortality after infant trauma remains underexplored. Infant trauma largely reflects the caregiving environment and should be examined separately from older ages.

To investigate whether biological sex is associated with in-hospital mortality among infants with trauma and describe patterns of infant injury in Japan.

This retrospective, observational study used data from the Japan Trauma Data Bank, a nationwide registry. It included infants (<1 year) who sustained trauma between 2004 and 2023. The exposure variable was biological sex. The primary outcome was all-cause in-hospital mortality. Multivariable logistic regression was adjusted for year of injury (categorized into 4-year intervals) and major trauma.

Among 1135 infants (63.8% male), blunt injuries predominated (95.6%), and falls accounted for 70.4% of incidents. Approximately 80% of cases with major trauma involved moderate-to-severe traumatic brain injury (TBI; Abbreviated Injury Scale ≥ 3). Overall, 51.5% were admitted directly to the intensive care unit. All-cause in-hospital mortality was 2.7% (3.0% in males vs. 2.2% in females). Multivariable analysis showed no significant association between sex and mortality (adjusted odds ratio for females, 0.94; 95% confidence interval, 0.40-2.03).

In this nationwide cohort of infants with trauma, there was no statistically significant difference in in-hospital mortality between biological sexes, supporting sex-independent approaches for acute trauma care. Most major trauma involved moderate-to-severe TBI, with falls being the leading cause of injury. Simple, broadly applicable prevention strategies, especially fall prevention, may help prevent infant trauma.