Introduction

Identification of factors that increase risk of, or are protective against, sudden infant death syndrome (SIDS) has largely been accomplished through epidemiological case-control studies. Risk factors include side and prone positioning, prenatal and postnatal tobacco smoke exposure, sleeping on soft or cushioned surfaces (particularly sofas, couches, and armchairs), bed sharing, soft bedding, head covering and overheating, and prematurity. Protective factors include breastfeeding, pacifier use, and room sharing. In this chapter, we will discuss the evidence for these risk and protective factors. We will also review the leading theories for SIDS causation including the Triple Risk Hypothesis, rebreathing theory, and deficient arousal and autonomic regulation, and how these theories create a plausible explanation for the risk and protective factors for SIDS identified in casecontrol studies.

Risk Factors

Side and prone sleep position

The prone sleep position was noted in multiple case-control studies to be associated with SIDS (1-6), beginning in 1965 in the United Kingdom (UK) (7). Even before this, in 1944, Abramson reported that prone positioning was found in 68% of young infants who died of accidental mechanical suffocation in New York City (8). Public health campaigns, which first promoted non-prone positioning in the 1980s and then supine placement, only beginning in the 1990s in many Western countries, have all been associated with a decline in SIDS rates. Subsequent studies have confirmed the association of prone sleep positioning and an increased SIDS risk (adjusted odds ratio [aOR] 2.3-13.1) (9-11). Physiologic studies have demonstrated an association of prone positioning with an increased risk of hypercapnia and hypoxia (12-14), overheating (15), diminished cerebral oxygenation (16), altered autonomic control (17), and increased arousal thresholds (18).

Subsequent studies have identified that the risk of side sleep positioning is similar to that of prone positioning (aOR 2.0 and 2.6 respectively) (10). Side positioning also has a higher population-attributable risk than prone positioning (11), likely because many infants who are placed on their side are found prone (10). Placement in, or rolling to, the prone position, particularly when infants are unaccustomed to that position, places infants at extremely high risk of SIDS (aOR 8.7-45.4) (10, 19). Thus all caregivers, including childcare providers, family members, and friends, should place the infant in the supine position for every sleep.