Many studies have shown that placing a baby younger than 1 year old to sleep on his or her back is the most important thing parents can do to reduce the risk of sudden infant death syndrome (SIDS). Since 1992, the number of babies who sleep on their back has gone up (due mostly to the national "Back to Sleep" campaign), and there has been a steady drop in the SIDS rate.1
Placing babies to sleep on their backs reduces the risk of SIDS. Side sleeping was also recommended in the past, but it is much easier for babies to roll to their stomachs from their sides than from their backs. Unless your doctor advises otherwise, do not place your baby to sleep on his or her side or stomach.
In rare cases, a doctor may recommend a different sleeping position if your baby has certain health problems.
As babies mature, they learn to roll from their backs to their stomachs. Babies who roll onto their stomachs during sleep do not need to be continually shifted onto their backs. But always initially place them to sleep on their backs.
When your baby is awake and someone is watching, allow your baby to spend some time on his or her stomach ("tummy time"). This may be good for the baby's development and may help prevent flat spots on the back part of the head.