Sudden unexpected death in infancy (SUDI) includes sudden infant death syndrome (SIDS). Co-sleeping is regarded as a major risk factor for SIDS. Under normal circumstances, nucleated red blood cells (nRBCs) are absent from the peripheral blood and their release can occur in cases with a probable hypoxic mode of death. The aim of our study was to assess the significance of the release of nRBCs in SIDS occurring during co-sleeping and the association with hemorrhages in the dura and the lungs. 35 cases were retrospectively assigned to one of the following categories: (I) 9 SUDI (of various causes) with no co-sleeping; (II) 16 SIDS while co-sleeping; (III) cause of death in hypoxic circumstances (3 hangings, 2 cardiac malformations, 1 meningitis 1 intoxication with diazepam); (IV) 3 SIDS in the cot. nRBCs were present in 5/9 cases of Category I (mean: 0.5%); 10/16 cases of Category II (mean: 1.87%); 7/7 cases of Category III (mean: 3.8%) and 0/3 cases of Category IV (mean: 0). ANOVA one-way test showed a significance of 0.003 amongst the 4 groups. The presence of diffuse intra-alveolar hemorrhage was associated with a higher release of nRBCs (mean: 3.1%) than focal hemorrhage (mean 0.6%). nRBCs were associated with focal hemorrhages in the falx and tentorium (mean: 2.3 vs. 0.9% when no hemorrhages were seen). The high mean of nRBCs seen in the co-sleeping SIDS cases suggests a higher exposure to hypoxia in the co-sleeping group which may have led to the release of nRBCs. More cases need to be analyzed to confirm this hypothesis.

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