4-month sleep regression

The Four Month Sleep Regression

As a professional Baby Sleep Consultant, I hear the term ‘regression’ used in regard to just about every imaginable circumstance. Essentially, if baby doesn’t sleep well for a couple of nights, parents start dropping the ‘R’ word. Some people subscribe to the idea that there’s an 8-month regression, a 9-month regression, a 1-year regression, as well as teething regressions, growth spurt regressions, and so on. Others see these as simple hiccups caused by extenuating circumstances.

But the 4-month sleep regression, it’s scientifically proven to be real. It is caused by a biological change for baby – but don’t worry, it does get better.

In order to understand what’s happening to your baby during this stage, first you need to know a few things about sleep in general. So, here’s the science-y part, but in layman’s terms so to speak.

Many people think of sleep as an on-or-off situation. You’re either asleep or you’re not. But sleep actually has a number of different stages. These stages make up our sleep cycle, which we go through several times a night. 

Stage 1

Thisis that initial stage we’re all familiar with where you can feel yourself drifting off, but don’t really feel like you’ve fallen asleep. Anyone who has ever seen their partner nodding off in front of the TV, told them to go to bed, and gotten the canned response of, “I wasn’t sleeping!” knows exactly what this looks like.

Stage 2

This is the stage which is considered the first ‘true sleep’ stage. This is where people tend to realize, once woken up, that they actually were sleeping. For anyone taking a power nap, this is as deep as you want to go, or else you’re going to wake up groggy.

Stage 3

This stage is deep and regenerative. Also known as slow wave sleep, this is where the body starts repairing and rejuvenating the immune system, muscles tissue, energy stores, and sparks growth and development.

Stage 4 

This stageis also called REM (rapid eye movement) sleep. This is where the brain starts to kick in and consolidates information and memories from the day before. It’s also the stage where we do most of our dreaming.

Once we’ve gone through all of the stages, we either wake up or come close to waking up, and then start over again until the alarm goes off.

So, what does this have to do with the dreaded 4-month sleep regression we were talking about above?

Well, newborn babies only have 2 stages of sleep: Deep Sleep and REM Sleep. They spend about half their sleep in each stage. Around the third or fourth month of life, there is a reorganization of sleep, as they embrace the 4-stage method of sleep that they’ll continue to follow for the rest of their lives. 

When this change takes place, baby moves from 50% REM sleep to 25% in order to make room for those first two stages. Although REM sleep is light, it’s not as light as these two new stages that they’re trying to get used to. With more time spent in lighter sleep, there’s a much higher chance that baby is going to wake up. 

That’s not to say that we want or need to prevent or avoid baby waking up. Waking up is absolutely natural. It is just how our bodies work and we continue to wake up three, four, five or more times a night into adulthood and even more in old age. 

What happens when we wake up during the night

As adults, however, we’re able to identify certain comforting truths that baby might not be quite as awake of. When we wake in the night, we’re able to recognize, “I’m here in my bed, it’s still nighttime, my alarm isn’t going to go off for another three hours, and everything in my environment is the same as when I went to bed. I can go back to sleep”

And back to sleep we go. Usually so quickly that, the next morning, we don’t even remember thinking about how we can go back to sleep or the brief periods we were awake. 

A 4-month-old baby, of course, lacks these critical thinking skills. To a 4-month-old baby who fell asleep at her momma’s breast, the thoughts could go much more to the tune of, “OK, when I feel asleep, I was cuddling with my momma, while eating my favorite food. Now I’m alone and everything it is completely different.” 

You can compare this to if you went to sleep in your nice comfy, cozy bed and all of a sudden you wake up and realize you are out on your front lawn. You are going to be pretty alarmed.

Now that baby suddenly realizes that Momma is not around, and they’re not entirely sure where Momma has gone, the natural response is to be alarmed or even a bit freaked out. That stimulates the fight-or-flight response and, next thing you know, baby is not going back to sleep without a significant amount of reassurance that everything is alright.

Another factor causing struggles with the 4-month sleep regression

The other major contributor to this 4-month sleep regression fiasco, I find, is that up until this point, parents have either been putting their baby to sleep with a pacifier, or by rocking them, or by breastfeeding them, or some similar technique where baby is significantly helped along on the road to falling asleep. 

Now that baby is spending more time in light sleep, and therefore has a higher probability of waking up, this suddenly becomes a much bigger issue. These sleep props or sleep associations can be very sneaky indeed. Although they may be helpful in getting your little one to sleep initially, the lack of the same sleep props when they wake up means that baby is not able to get back to sleep again without some outside help. Cue the fight-or-flight, the crying, and the adrenaline responses. When this starts happening every half an hour, parents can understandably find themselves in a nightmarish situation.

Some good news about the 4-month sleep regression

So, some good news for anyone experiencing the dreaded 4-month sleep regression is that it’s not, in fact, actually a regression at all. A regression is defined as “reversion to an earlier mental or behavioral level,” and that’s actually the opposite of what your baby is experiencing. They are experiencing a sleep progression, as sleep cycles begins to mature. But I’m betting that good news probably doesn’t make a parent in the midst of this change feel better in the slightest. In terms of the amount of wake ups baby is having and the amount of sleep parents are getting, this definitely feels like a regression.

The cause of the 4-month sleep regression is a real biological and permanent change. This brings up to the big question: What can you do to help your little one adjust so the pain and sleep deprivation doesn’t start to feel permanent?


First off, get all of the light out of baby’s room. I’m not kidding around here. You might think that baby’s room is dark enough, or that baby might not like the dark, and that it’s comforting to have a little bit of light coming through the windows or seeping in from the hallway. 

Nope. That’s a big fat NOPE.

Baby’s room should be dark, dark, dark! I mean coal mine on a moonless night kind of dark. Tape garbage bags over the windows, cover them with tinfoil, whatever you have to do. 

Newborns and infants are not afraid of the dark. They lack the cognitive capacity to imagine scary things in the dark. However, they are very responsive to light. Light tells their brains that it’s time for activity and alertness, and the brain secretes hormones accordingly, so we want to keep their nursery pitch black during naps and bedtime. When baby has a reaction to their newly darkened room it is usually related to the change itself, not being scared of the dark.


The other nemesis of daytime sleep, (and nighttime for that matter, although not nearly as often) is noise. Whether it’s the Amazon delivery person ringing the doorbell (it’s cool you don’t need to ring the doorbell, my app alerts me that you delivered my package), or the dog warning you that the squirrels are back and for sure going to attack the house this time (yup, this is absolutely the time we are all in real danger, thanks for letting me know!), or something falling on the floor three rooms away, there is always some noise that can wake up baby. With baby spending more time in lighter sleep, noises will startle them easily and wake them up, so a white noise machine is a great addition to your nursery. 

Wait, isn’t that a prop? Well, in a way, it is, but it doesn’t require any winding, resetting, reinserting, or parental presence. It’s just there and it can be on as long as baby’s sleeping, so it’s not a prop we need to avoid. It can actually be a great sleep cue, something that babies recognize only happens when it is time to transition to sleep. Sound is one of the strongest sleep cues for babies. 


Bedtime routines are also an essential component to getting your baby sleeping well. Try to keep the routine to about 4 or 5 steps, and don’t end it with a feed. Otherwise, you risk baby nodding off at the breast or the bottle, and that will create the dreaded association that we talked about earlier. 

Try to keep the feed near the beginning of the routine so they can fill their tummies while wide awake. Then plan on getting into cozy pajamas, singing some calming songs and reading stories towards the end. The whole process should be about 20 to 30 minutes long, and baby should go into their crib while they’re still awake. 

If you’re noticing baby getting fussy before bedtime or during their bedtime routine, you probably waited too long. Four-month-old babies should really only be going about two hours between snoozes, and bedtime should be between 7 and 8 at night.

What about going forward after the 4-month sleep regression?

Now, there are going to be regressions, actual regressions, later on in your little one’s childhood. Traveling, illness, cutting teeth, all of these things can cause your little one to have a few bad nights in a row. But when it comes to the 4-month progression, I’m happy to report that this is a one-time thing. Once you’re through this, your baby will have officially moved into the sleep cycle pattern that they’ll essentially be following for the rest of their life. Four glorious stages repeated multiple times a night. 

By taking this opportunity to teach them the skills they need to string those sleep cycles together, independently and prop-free without any need for nursing, feeding, rocking, or pacifiers, you will give them a gift that they’ll enjoy for the rest of their lives.

Of course, some kids are going to take to this process like a fish to water, and some are going to be a little more resistant. If yours falls into the former category, count yourself as lucky and take delight in your success! 

For those of you in the latter camp, I’m happy to help in any way I can. Reach out and we can create a personalized program for your little one to help them learn the skills to sleep independently. The most common thing I hear after working with clients is, “I can’t believe I waited so long to get some help!” If you’re exhausted and at your wits end, now is absolutely the time. Let’s get on a free call so I can learn more about your little one’s situation and we can move forward as soon as you’re ready to get your little one sleeping well and through the night!

Cheers to healthy, happy sleep!

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