Have you ever wondered why newborn vs baby vs adult sleep all looks so different?! Wouldn’t it make sense if we all just were born with the same sleep habits, so no one misses out on sleep?
Unfortunately, that’s not the case. As we all know.
But, if we know a little more about the science behind our children’s sleep, then we can at least check that off the list of “Things to Wonder About as a Parent”.
To really understand what happens when our babies sleep, let’s look at the different stages of sleep that occur in a sleep cycle.
The two main terms for stages of sleep are REM (rapid eye movement or active sleep) and NREM (Non-rapid eye movement or quiet sleep).
REM sleep is a light stage of sleep where your baby may make small movements, their eyes will move around under their eyelids, you may notice some twitching in their limbs, and their breathing becomes rapid and slows down and then picks back up again. This is also when they may make lots of noise such as grunting.
NREM sleep is broken into 3 different stages. They are:
NREM 1: Light sleep- transition from wake to sleep
NREM 2: Light sleep but drifting to deeper- heart rate slows, body temperature drops
NREM 3: Deep sleep- difficult to wake up
For newborn babies, they spend their time sleeping equally divided between REM and NREM Stage 3. Which means they are either in active sleep sounding like a freight train in the bassinet next to you or they are in a deep sleep.
This is also why it seems like newborns can sleep through any noise. They spend 50% of the time that they are asleep in a deep state of sleep.
At around 3 or 4 months old, their sleep cycle changes to include 2 more stages of sleep. This will be the cycle that they follow into adulthood. But the difference is the amount of time that they spend in each stage is less compared to the amount of time adults spend in each stage of sleep.
Most people know of this change in sleep as the 4 Month Sleep Regression. Once this happens, your baby cycles through the 3 stages of NREM sleep and REM sleep in about a 50-60 minute period (fun fact: during the day, this cycle is a bit shorter at 45-50 minutes).
Therefore, they spend more time in a light stage of sleep than they did as newborns. As adults, it takes us around 90 minutes to complete a sleep cycle. Around 5 years old, children’s sleep cycles begin to mirror the length of adult cycles.
A baby’s sleep cycle is broken out like this:
Falling asleep light sleep: 0-10 minutes. Can be easily woken
Getting deeper light sleep: 5-15 minutes
Deep Sleep: 20-30 minutes
REM: 10 minutes in the first sleep cycle but can increase with each sleep cycle
So, how can this information be useful to us, as parents?
1. I think it’s important to help us cope with the “why won’t this baby sleep?” frustration. Especially with newborns. Newborns are not born with their circadian rhythm. Add that to their tiny bellies and shorter sleep cycles and it’s no wonder that they wake frequently through the night.
2. When a sleep transfer is necessary (from arms to crib or car to crib or arms to stroller), it’s helpful to keep an eye on how long they’ve been asleep for. If you can wait for about 10-20 minutes, you’ll have a higher chance of a successful transfer.
3. Understanding the cycle helps us understand why short naps are happening. If your child is consistently waking
at the 30–45-minute mark, they are most likely not completing a full sleep cycle and not able to connect two sleep cycles together.
4. This information also shows us why teaching sleep can be so important if the baby doesn’t develop the skill on their own. If your child wakes at the end of one sleep cycle and is calling out to you, they don’t know how to get themselves from that lighter stage of sleep that their cycle ended with to the next cycle. Once they develop that skill, their sleep stretches at night and their naps tend to lengthen.
5. Simply being 'in the know' is a stress reliever. When we don’t understand something that is happening, we tend to guess. We wonder if it’s teething, or sickness, or they’re too cold, or too hot, or they hate the sleep sack, or the mattress is not comfortable. This constant state of wondering what
is going on can wreak havoc on a parent’s mental health. When we understand why things are happening, it helps us cope with it much easier.