This is possibly the most prominent and discussed regression and it's pretty rare for a parent not to experience it. But why does it occur?
It's important to note that while it is commonly coined the 4 month sleep regression, this change can actually occur anytime between 3 and 6 months.
The predominant cause is the maturation of the baby's sleep cycle. So they are literally changing the architecture of their sleep, which understandably could be a little jarring for your small one.
REM sleep, also known as dreaming sleep, is paramount for brain maturation and the formation and processing or memories. This is probably why newborns spend 80% of their sleep in REM and the rest of the time in NREM3/4, which is the deep, quiet sleep.
What we don't see in the newborn months are NREM 1 + 2. These are the lighter stages of quiet sleep and during this time one is easily roused. These states create a nice transition from being awake to falling deeply asleep.
A newborn sleep cycle looks a bit like this...
REM – NREM3/4 – REM – NREM3/4 etc
Then as it develops it forms this shape...
NREM1 – NREM2 – NREM3/4 – NREM2 – NREM1 – REM – NREM1 etc
As your little one's sleep cycle matures and they are introduced to a more complex sleep architecture it is common to experience some difficulties -
Frequent night wakings.
Startling awake soon after falling asleep as they transition into a deeper sleep. This can give the feeling of falling out of bed.
Difficulty with naps either being shorter or missed all together
Harder to settle at bedtime.
All of these can lead to fussier and crankier babies.
A couple of other tricky little developments happen at this age that can exasperate the situation somewhat...
As babies become more aware and alert they in turn become more easily distracted. This can disrupt daytime feeds and lead to them wanting to feed more at nighttime. You could try wearing a nursing necklace while feeding to keep them focused on the right area. Alternatively, feeding as soon as they wake up, while they are calm and in a quiet place can help optimise those day feeds.
Over the full range of 3-6 months your baby's sleep need will decrease and they may drop a nap in the latter half of this period. This can sometimes bring it's own challenges with finding the right balance for you and your little one. A little trial and error with timings and reading your baby's sleep cues can work wonders.
This time can be really hard. I feel you. You may have just started to feel like you are really getting into your groove and getting some consolidated nighttime hours sleep and then suddenly it's all moving backwards. But...
It will pass. I promise.
It is developmentally normal and your little one just needs a little practice at transitioning through their new cycles.
Of course, if you are worried about anything and are struggling then hop over to my contact me page and drop me a message and we can discuss working together to make any changes you need. Or have a look at my packages to see what I offer.