Full term newborn babies sleep up to 16 to 20 hours a day and cannot seem to differentiate between day and night. A premature baby on the other hand would sleep anywhere between 20 to 22 hours. But the flip side about baby sleep is that they don't sleep for all those hours at a stretch. Babies have a 40 minutes sleep cycle and spend most of it in REM sleep or Rapid Eye Movement. In a REM sleep a baby will suck grimace smile and occasionally twitch their fingers and toes. They wake up every 3 to 5 hours