What is a significant risk factor for sudden infant death (SID)?

The significant risk factor for sudden infant death (SID) among the options given is parental smoking. Research has consistently shown that infants who are exposed to tobacco smoke, either during pregnancy or after birth, are at a higher risk for sudden infant death syndrome. This is attributed to several factors, including the effects of nicotine and other harmful chemicals found in cigarettes, which can affect the infant's ability to regulate their heart rate and breathing while sleeping.

While low birth weight, respiratory infections, and the disturbed symmetry of the atlanto-occipital region could have implications for an infant’s health, the established association between parental smoking and SID makes it a recognized and critical risk factor. The evidence supporting the dangers of parental smoking includes epidemiological studies that have shown a correlation between maternal cigarette use and an increased incidence of SID, reinforcing the importance of creating a smoke-free environment for infants.