Baby Sleep Cycle Science
Updated: Nov 14, 2021
...a baby's nap continues to be be short and stays at 45 minutes if they cannot link to another sleep cycle. Sleep props (ie. pacifiers, rocking, feeding, car rides, etc.) are infamously known to be major culprits for these 45-minute naps.
Stages of Sleep
Many of us just think of sleep as an on-or-off situation. You’re either asleep or you’re not. But sleep actually has a number of different stages, and they make up the “sleep cycle,” which we go through several times a night. So here’s the science-y part, told in plain English.
Stage 1 is that initial stage we’re all familiar with where you can just feel yourself drifting off, but don’t really feel like you’ve fallen asleep. Anyone who has ever seen their partner nodding off in front of the TV, told them to go to bed, and gotten the canned response of, “I wasn’t sleeping!” knows exactly what this looks like.
Stage 2, is a lighter stage of non-REM (rapid eye movement) sleep. This is where people tend to realize, once woken up, that they actually were sleeping. For anyone taking a “power nap,” this is as deep as you want to go, or else you’re going to wake up groggy.
Stage 3 deep and regenerative, non-REM sleep. This is where the body starts repairing and rejuvenating the immune system, muscles tissue, energy stores, and sparks growth and development.
Stage 4 deep, REM sleep is where the brain starts to kick in and consolidates information and memories from the day before (long term memory storage). This stage of sleep helps manage emotion like anxiety, depression and pain. It’s also the stage where we do most of our dreaming.
Once we’ve gone through all of the stages, we either wake up or come close to waking up, and then start over again into the next sleep cycle until the alarm goes off.
Sleep Cycles for Babies
A one year old has a sleep cycle that is 45 minutes in length and will lengthen as they age until they have adult sleep cycles that are 90-110 minutes long. Younger babies have even shorter sleep cycles. For this reason, one of the most common complaints I hear from parents is that their baby only takes 30-45 minute cat naps.
What happens, is a baby's nap continues to be be short and stays at 45 minutes if they cannot link to another sleep cycle. Sleep props (ie. pacifiers, rocking, feeding, car rides, etc.) are infamously known to be major culprits for these 45-minute naps.
For a deep dive into the health benefits of getting continuous sleep cycles, check out this killer article with the juicy details: The Power of Sleep: How Much Sleep Is Enough Sleep and Why?
Do Baby Sleep Cycles Change Over Time?
Newborn babies only have two stages of sleep; quiet and active sleep REM (rapid eye movement). When babies reach the 4 month sleep regression, their sleep becomes more adult-like and evolve into 4 stages of sleep. This means baby now has acquired 2 lighter stages of sleep. Baby now spends more time in lighter sleep, thereby creating more chances of night wakings.
So if you're a parent whose baby slept like an angel for the first few months but suddenly realized your baby is now fighting sleep, won't transfer well to the crib or wakes multiple times at night with no end in site, you've more likely than not hit the famous four month sleep regression.
Check out my post, "Does the Four Month Sleep Regression Really Exist" if you feel like your baby's sleep habits have made a 180º on you. And for those still stuck in the four month sleep regression wheel, check out my post on Troubleshooting the 4 month Sleep Regression.
If you find the complexities of baby sleep overwhelming and your efforts spent troubleshooting their sleep frustrating, I'm always here to help.
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