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The 4 month "Sleep Regression": A permanent change to baby's sleep architecture

Updated: Aug 30, 2023

A sleep regression is a period of time (usually lasting about 2-4 weeks) when a baby who was sleeping well unexpectedly resists sleep, has trouble settling down for sleep and/or wakes often after falling asleep.

Most sleep regressions are caused by illness, teething and/or developmental milestones (rolling, sitting, standing, etc). But the 4-month sleep regression is slightly different from the other regressions because it’s biologically driven- as your baby’s brain matures, her sleep is reorganizing to become more adult-like and the change is permanent.

To better understand how this happens, we’ll have to delve a little into the science of sleep.

If its not a true regression, what is it?

Sleep is often thought in binary terms- you’re either asleep, or awake. But the truth is that even in sleep, we cycle through stages of light sleep and deep sleep many times in the course of a night.

As depicted in the diagram above, adults have a 4-stage cycle (Stage 1, 2, 3/4 and REM). This is contrast to babies under 3 to 4 months of age, who only experience 2 stages of sleep— Stage 3/4 and REM— and spend about 50% of their time in each stage. It’s worth noting here that although REM sleep is light, it’s not as light as Stages 1 and 2 of sleep in the 4-stage cycle. This explains why your newborn slept through even the loudest of rackets, or (in some cases) even slept through her diaper change!

However, once baby graduates from the 2-stage cycle she was born with to the 4-stage cycle, she moves from 50% REM sleep to 25% in order to make room for the new Stages 1 and 2. With more time spent in light sleep, there’s more of a chance baby will be woken up by environmental factors like loud noises and light. This is in addition to the biologically normal “brief awakenings” that take place as all of us transition from one sleep cycle to another.

When baby wakes up (whether because she was roused, or in between sleep cycles), depending how she is accustomed to falling asleep, she’ll either cry out for assistance to fall back asleep or soothe herself back to sleep.

Adding some further complexity to this is also the fact that round about this time your baby experiences a cognitive surge which makes her much more aware of her surroundings and you. You’ve probably noticed her smiling and laughing at you to keep your attention. It is also at this stage that she will want you in the middle of the night, or believe she cannot fall sleep without your assistance and/or presence. And this development could potentially cause major disruptions to yours and her sleep.

Now, on to the big question— how can you help your little one to adjust to her new norm?

Ways to ride out the hump

1) Keep it dark and quiet

Your baby’s room should be dark- I mean coal mine on a moonless night kind of dark. To achieve this, tape construction paper over the windows if you have to.

You may not realise but your baby is actually really responsive to light- melatonin is secreted even when there’s an indirect light source, which tells baby’s body it’s time for activity and alertness, the exact opposite state of what we want to achieve for naps and overnight sleep.

The other nemesis of daytime sleep is noise. We’ve already alluded to the fact that baby spends more time in lighter sleep, so loud noises like a neighbour’s dog barking, the rubbish truck going by or the door bell will startle her awake. To minimize wake-ups, a white noise machine could help to drown out ambient noise.

2) Honour baby’s awake window

Keeping baby awake beyond her tolerance levels will result in overtiredness that builds and manifests in more wake-ups. The reason for this is because overtiredness causes our bodies to release cortisol, the stress hormone that keeps our bodies alert and ready to go, thereby making falling asleep and staying asleep that much harder.

3) Implement a bedtime routine

If you haven’t already, start a bedtime routine for baby. This will cue her brain to transition from being awake to being asleep. The power of a routine should not be underestimated- think about your own habits before going to sleep. Most adults are actually quite protective of their routines before sleep. If you miss a step in your routine, you’d probably take a longer time to fall asleep than you otherwise would.

When setting up your routine for baby, one thing to avoid is feeding just before bed. This prevents a feed-sleep association from forming, where baby thinks she needs to nurse in order to get drowsy.

4) Consider teaching baby to fall asleep independently, if you haven’t already

Now is the perfect time to teach your child the skills they need to string those sleep cycles together independently. As with all things, some kids will take to the process like a fish to water, and others not.

For those of you in the latter camp, we’re happy to help in any way we can. Just book a discovery call with us and we can see how we can build a more personalized programme for your little one to get them on the path to independent sleep.

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