Objective: The risk of sudden infant death syndrome (SIDS) among infants who co-sleep in the absence of hazardous circumstances is unclear and needs to be quantified.
Design: Combined individual-analysis of two population-based case-control studies of SIDS infants and controls comparable for age and time of last sleep.
Setting: Parents of 400 SIDS infants and 1386 controls provided information from five English health regions between 1993-6 (population: 17.7 million) and one of these regions between 2003-6 (population:4.9 million).
Results: Over a third of SIDS infants (36%) were found co-sleeping with an adult at the time of death compared to 15% of control infants after the reference sleep (multivariate OR = 3.9 [95% CI: 2.7-5.6]). The multivariable risk associated with co-sleeping on a sofa (OR = 18.3 [95% CI: 7.1-47.4]) or next to a parent who drank more than two units of alcohol (OR = 18.3 [95% CI: 7.7-43.5]) was very high and significant for infants of all ages. The risk associated with co-sleeping next to someone who smoked was significant for infants under 3 months old (OR = 8.9 [95% CI: 5.3-15.1]) but not for older infants (OR = 1.4 [95% CI: 0.7-2.8]). The multivariable risk associated with bed-sharing in the absence of these hazards was not significant overall (OR = 1.1 [95% CI: 0.6-2.0]), for infants less than 3 months old (OR = 1.6 [95% CI: 0.96-2.7]), and was in the direction of protection for older infants (OR = 0.1 [95% CI: 0.01-0.5]). Dummy use was associated with a lower risk of SIDS only among co-sleepers and prone sleeping was a higher risk only among infants sleeping alone.
Conclusion: These findings support a public health strategy that underlines specific hazardous co-sleeping environments parents should avoid. Sofa-sharing is not a safe alternative to bed-sharing and bed-sharing should be avoided if parents consume alcohol, smoke or take drugs or if the infant is pre-term.