Our babies change so much in their first months of life – they go from sleepy babies that mainly eat, sleep and poop to happy, alert babies who love to spend time playing and engaging with their parents and can fight sleep just for more snuggles or struggle get to sleep without rocking, feeding or the pacifier.  Learning the science of baby sleep can really help us as parents understand why babies sleep the way they do and why they can struggle. science of baby sleep

When babies are born their internal clocks aren’t synchronized with the normal 24-hour day.   They aren’t able to differentiate between day and night.  Anyone heard of day and night confusion?  This is why some babies can be more awake overnight or just sleep the same amount no matter the time of the day.  As they get closer to 6 weeks old they tend to start sleeping a longer stretch overnight, starting with about 4 – 6 hours. science of baby sleep

science of baby sleepSleep changes around 4 months old.

It isn’t until a baby hits 3 – 4 months old that their sleep becomes more adult like.    They start to produce melatonin around this time.  Melatonin is a naturally produced sleep hormone.  The levels are highest in the evening hours because of the darkness, which helps trigger our brain that we need to sleep. science of baby sleep

Instead of falling straight into deep sleep, like newborns do, they first fall into light sleep.  This is why babies often experience the 4-month sleep regression – because they have to learn how to transition between sleep cycles.   Parents often find that their baby who used to fall asleep while being held and transfer to the crib; can’t make that transition any more because they get woken easily when transferred into the crib. science of baby sleep

Babies after 4 months of age can also start to push themselves to stay awake and fight much needed sleep to enjoy the pleasure of their parents company.  This is why it becomes very important to be very strict with your sleep schedules and routines – to ward off overtiredness.  Just because your baby doesn’t seem sleepy, doesn’t always mean that they don’t need to go to sleep.  They might just be enjoying you too much to show those sleepy cues.

Overnight sleep.

Babies naturally experience many brief arousals throughout their night of sleep.  As adults we do too, but for us we may just adjust our pillows, move a blanket and fall back to sleep.  For babies they may make some noise while transitioning back to sleep, or cry out to their parents signaling for help.  They often signal if they are not yet used to helping themselves get to sleep and back to sleep (think sleep association). science of baby sleep

Baby sleep vs. adult sleep.

A baby’s sleep cycle differs from that of adults.  An average adult sleep cycle is around 90 minutes, where as a baby’s sleep cycles are around 50-60 minutes for the first 9 months of their life.  During the REM stage of sleep (the light sleep at the start of the sleep cycle) an infant’s brain is developing and consolidating cognitive and physical skills that they have learnt throughout their awake periods. science of baby sleep


Naps are incredibly important for babies and having one nap doesn’t compensate for another.  There is more REM sleep in the morning nap, which helps with brain maturation and mental and emotional restoration.  There is more deep sleep in the afternoon nap, which makes it more restful and physically restorative.  This means that it is important to prioritize both naps for completely different reasons. science of baby sleep

As you likely know, newborn babies sleep anywhere, anytime and for varying lengths of time.  But often around 4 months their naps are short as they learn to cope with the change to their sleep cycles.  The morning nap is the one that usually starts to extend first into a nice long restorative nap, and then the midday nap after that.

Helping your baby sleep.

As much as a little newborn makes sleep look easy, past the newborn phase babies may not be able to go to sleep easily and fall back to sleep at awakenings overnight.  This is why establishing healthy sleep habits from early on, helps them transition to more adult like sleep at around 4 months.  Although this doesn’t always guarantee you are spared the 4 month regression, sorry!  You can help your baby sleep by ensuring your baby naps and goes down for the night at the right time, teaching him/her to fall asleep on their own, and providing the best environment for safe restorative sleep.

science of baby sleep



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