A combination of physical and sleep environmental factors can make an infant more vulnerable to SIDS. These factors may vary from child to child. Physical factors Physical factors associated with SIDS include: Brain abnormalities. Some infants are born with problems that make them more likely to die of SIDS. In many of these babies, the portion of the brain that controls breathing and arousal from sleep doesn't work properly. Low birth weight. Premature birth or being part of a multiple birth increases the likelihood that a baby's brain hasn't matured completely, so he or she has less control over such automatic processes as breathing and heart rate. Respiratory infection. Many infants who died of SIDS had recently had a cold, which may