SIDS is an acronym for Sudden Infant Death Syndrome, and is used to describe what happens when an infant suddenly dies with no apparent cause. SIDS causes an very small amount of deaths, though it is the leading cause of death among infants over one month of age. The cause is unknown, though several risk factors have been identified. These include, inadequate prenatal care, inadequate prenatal nutrition, use of heroin, cocaine and other drugs, subsequent births less than one year apart, alcohol use, infant being overweight, mother being overweight, Teen pregnancy (if the baby has a teen mother, it has a greater risk), infant's sex (60% of SIDS cases occur in males). Being prematurely born increases risk of SIDS 4 times higher than normal. Apparently using a fan to circulate air in the bedroom reduces risk 72%,only 3% of mothers, reported having a fan on during the babies death. Babies co-sleeping, or sleeping with a parent, are said to have increased risk of Sudden Infant Death Syndrome.
Information taken from Wikipedia.org and 8th grade health class.