The Four-Month Sleep Regression

Let’s talk sleep regressions. I hear from parents all the time who attribute their little one’s sleep problems to this regression or that regression. And, yes, there is some truth to regressions causing upsets in sleep; but just because they exist doesn’t mean that you have to throw up your hands and resign to sleepless nights. You’re not stuck with a poor sleeper; there are things you can do to help you navigate regressions.

Most regressions are attributable to milestone achievements and reorganization of the body and the brain. The most common regression I hear about is the four-month sleep regression, so I want to take some time to break down what exactly is going on developmentally around this time and why your previously angelic sleeper is now keeping you up all night.


The Science Behind The Four-Month Regression

When babies are born, their sleep is drastically different from the sleep of adults. Newborns really only have two stages of deep sleep whereas adults have four stages ranging from very light to very deep. The organization of infant sleep also differs from that of adults: As we all know, infants do not sleep in consolidated ways and are essentially on a 24-hour clock consisting of periods of sleep and awake for the first few months of life. As infants develop, sleep becomes more consolidated and they are able to sleep for longer periods at a time (hopefully at night!)

Obviously, since adult sleep is not organized this way, infant sleep has to shift to a more mature form at some point. Guess when that happens? Yep, around the third or fourth month of life. At this time, there is a reorganization of sleep and during this reorganization, the body and the brain must work hard to make these changes happen. Therefore, it’s totally conceivable that some infants struggle to make this transition.


But why do some infants have such a hard time whereas others do not?

Because infants are now spending time in lighter stages of sleep, there is more potential to be woken during those times both from environmental noise and natural occurrences. Adults usually come to the surface of sleep every 90 minutes as they cycle through these stages. Sometimes this causes a partial-awakening that we don’t remember the next morning, and sometimes, something (a dog barking, your partner moving in bed, a car alarm going off) wakes us up fully and we get up to use the bathroom or get a drink of water before heading back to bed.

The same is true for infants. They will begin to come to the surface of sleep every 90 minutes as well. But let’s say you nursed your little one to sleep and put them down in their crib once you were sure they were deeply in dreamland. If they then awaken between their cycles, even briefly, and are in a situation that is vastly different than the one they fell asleep in, that is going to be startling and cause a full-blown wake-up instead of a simple transition into another sleep cycle. Also, around this time, there is a cognitive surge and infants become much more aware. That means that those infants who rely heavily on external strategies to fall asleep (nursing, rocking, bouncing, etc.) are more likely to protest when those things are absent during the night. They strongly believe they need those specific circumstances to be able to "make sleep come".

Up until now, you could have been sailing through, rocking your baby to sleep and everything had been fine. But, if your little one believes they need certain circumstances to fall asleep these developmental changes can cause major problems.

So now that you understand what is going on, what can you do? Here are a few things that I recommend during my private consultations to help encourage better sleep.


Managing the Four-Month Sleep Regression

+ Make the room dark

Darkness plays a huge role in cuing our body clocks to get in line with spending the majority of sleep at night time. That doesn’t mean there won’t be wake-ups, or a feed won’t be needed, but this will help to encourage sleep to come. Darkness will also cue the body to develop melatonin which will help baby sleep for longer stretches


+ Use a noise machine

Because baby is spending more time in a lighter sleep, white noise can block out any jarring environmental sounds that could pull a baby into full wakefulness.


+ Implement a bedtime routine

Routines cue the body and brain that lets us know that we are transitioning out of day and into the night. This is true for adults too (think about your bedtime routine, and even how you fall asleep: which side of bed you have to be on, what’s on your nightstand, what position you lay in, etc.)


+ Choose an early bedtime

Based on research, most infants’ body clocks trend towards a 7pm bedtime and a 7am wake-up, so don’t try to fight nature. And if you can get your little one down this early, think of all the free time you’ll have in the evening to do…whatever you want!


+Be aware of wake windows

Prior to this, your little one might have just fallen asleep whenever, wherever. Consolidated nighttime sleep is aided by honoring daytime sleep. Being cognizant of how long your little one can tolerate being awake will help to prevent over-tiredness which can lead to poor sleep quality. Around 4 months, infants can only tolerate about 1.5 – 2 hours of time awake before they are going to start to get over-tired.


+ Put baby down awake

This helps encourage your little one to fall asleep independently and prevents baby from thinking they always need someone or something else to fall asleep. We don’t want you to get stuck in a cycle where you’re going to have to come in throughout the night to recreate the situation that got baby to sleep in the first place!


+ If your baby cries out in the middle of the night, wait for a moment before going to them.

Their cries could just be them transitioning from one light sleep cycle to another and they are not actually fully awake and needing something. This also gives baby the opportunity to try to get back to sleep on their own


+ Hold them to their personal best!

Last but not least, give your little one credit where credit is due! If they showed you one night that they can sleep a five-hour stretch without needing a feed, then you want to encourage that because you know it’s possible.



Regressions are bound to happen. Oh Baby is here to help you navigate the extra tricky ones. Check out our Infant Sleep Package to get a handle on the four-month-sleep regression once and for all. If your child has previously been a great sleeper, visit our Mini Consultation for support with later regressions.