12 months. This is by definition. In my forensic pathology practice, most "sids" cases that i see have occurred in an unsafe sleep environment. Historically, many have been missed homicides, and a pathologist will always want to rule out everything from having been fed raw honey (botulism) to being born without sweat glands to mutated ion channels in the heart.
12 months old. Sids (sudden infant death syndrome), is most common in the first 6 months, but is used for any unexplained infant death in the first year. The risk of sids is reduced by having your baby sleep on her back, pacifier use, and background noise such as a ceiling fan. It can be increased by overheating and by the presence of tobacco smoke.