<P> The cause of SIDS is unknown . Although studies have identified risk factors for SIDS, such as putting infants to bed on their stomachs, there has been little understanding of the syndrome's biological process or its potential causes . The frequency of SIDS does appear to be influenced by social, economic, and cultural factors, such as maternal education, race or ethnicity, and poverty . SIDS is believed to occur when an infant with an underlying biological vulnerability, who is at a critical development age, is exposed to an external trigger . The following risk factors generally contribute either to the underlying biological vulnerability or represent an external trigger: </P> <P> SIDS rates are higher for infants of mothers who smoke during pregnancy . SID correlates with levels of nicotine and derivatives in the infant . Nicotine and derivatives cause significant alterations in fetal neurodevelopment . </P> <P> Placing an infant to sleep while lying on the stomach or the side increases the risk . This increased risk is greatest at two to three months of age . Elevated or reduced room temperature also increases the risk, as does excessive bedding, clothing, soft sleep surfaces, and stuffed animals . Bumper pads may increase the risk of SIDS due to the risk of suffocation . They are not recommended for children under one years of age as this risk of suffocation greatly outweighs the risk of head bumping or limbs getting stuck in the bars of the crib . </P> <P> Sharing a bed with parents or siblings increases the risk for SIDS . This risk is greatest in the first three months of life, when the mattress is soft, when one or more persons share the infant's bed, especially when the bed partners are using drugs or alcohol or are smoking . The risk remains, however, even in parents who do not smoke or use drugs . The American Academy of Pediatrics thus recommends "room - sharing without bed - sharing", stating that such an arrangement can decrease the risk of SIDS by up to 50% . Furthermore, the Academy recommended against devices marketed to make bed - sharing "safe", such as in - bed co-sleepers . </P>

When was the first case of sids reported