4 Month Sleep Regression Explained (sometimes 3 and 5 months too)

Over the years, our team has seen countless parents come to us for help with their 4 month old babies sleep. Why? Simple – it’s the 4 month sleep regression. This article will explain why “good” sleepers sometimes turn “bad” around the 4 month old mark, also known as the 4 month sleep regression. For most babies, the 4 month sleep regression occurs right around the 4 month mark, but for some babies, it happens a bit earlier (around 3 months) or a bit later (around 5 months). For some babies, the 4 month sleep regression is relatively mild and very brief; for others, the 4 month sleep regression is a very, very rough phase marked by lots of crying, and that lasts pretty much indefinitely.

Yes, this is an article about the 4 month sleep regression, so we really should be talking about 4 month old babies, right? We will, in just a moment – but first, we need to back up to the newborn phase. When a newborn sleeps, she cycles between “active” and “quiet” sleep (also known as REM and non-REM sleep), but does not have the distinctive stages of sleep she will have as she grows older and her brain matures. We’ll avoid too much technical talk (that’s one reason we have this website, so you won’t have to learn the whole history of sleep if you don’t want to (or can’t stay awake to!), but if you are interested in knowing more about our biological rhythms and how we do sleep in more detail, I highly recommend the book, Solve Your Child’s Sleep Problems), even if you have no interest in “Ferberizing” (just skip that part and consider a no-cry method). Newborns spend a lot of their time in deep sleep, which is why it is hard to wake them up (even to eat!) in those early days, but they do startle when they cycle into “active” sleep, which is one reason swaddling your baby can be so effective.

We all go in and out of light and deep sleep. As adults, we might change positions, look at the clock, or re-position our pillow. Up until now, you may have rocked your baby or simply given him a pacifier and he slept for hours without waking up. Well, at 3 or 4 months old, your baby is now sleeping more like an adult. Now when she falls asleep, she does not enter deep sleep right away, and if you lay her down before she is in deep sleep, she is likely to wake up and you will start all over helping her to fall back to sleep again and again.

Initially in the night, your 4 month old will enter deep sleep relatively quickly, within 30 minutes (this changes as we get older). However, as I said, we all cycle in and out of light and deep sleep. A child’s sleep cycle is about 40-50 minutes. So, your baby will briefly awake 40-50 minutes after she has been asleep. To put that in perspective, if you are holding your baby to sleep, you would need to hold her for at least 30 minutes to make sure she’s in deep sleep and then she might wake up 15 minutes later. Sound familiar?

Overall, though, your baby’s deepest sleep is in the early part of the night, so after that first sleep cycle, she might sleep just fine for a few hours. So, you’re golden, right? Just hold her for an hour? Nope!

The technical definition of “sleeping through the night” is 5 hours of continuous sleep (i.e. no feedings) and many babies can/will do this by 2 or 3 months old. The beginning of the night is your baby’s deepest sleep, and after the first 5 hours (if not sooner, depending on just how challenging he is), he will cycle between light and deep sleep, but the deep sleep won’t be as deep as it was at the beginning of the night. This is where the problem of sleep associations really come into play. If your baby needs your help to go to sleep at the beginning of the night, sometime after midnight or so, he will continue to need your help every 1 or 2 sleep cycles (that means every 40 to 90 minutes, or as I often hear: every 1-2 hours).

Between 4-6 a.m., approximately, is the lightest sleep of the whole night (parents’ complaints alone make this true, in my experience, aside from my reading). In the very early morning hours (about 30 minutes to an hour before waking up), he will again go into the very deep sleep.

Although babies commonly wake up early, be sure it is truly their waking up time and not just this lighter sleep and that they are having trouble sleeping. You might notice they want a “nap” just 30 or so minutes after “waking up”. What you experienced was a night waking, not starting the day.

4 Month Sleep Regression Symptoms

Many parents want to know what the 4 month sleep regression looks like. That will vary from baby to baby, of course, but here is a short list of 4 month sleep regression signs:

• Changes in appetite (baby may eat more or less than usual)
• Lots of night wakings (these will seem out of the ordinary, especially if your baby had been sleeping longer stretches recently)
• Increased crying and fussiness (often, the fussiness will be the inconsolable kind, and nothing you do to comfort your baby will work as well as it usually does)
• Missed naps and/or shorter naps

As we’ve established, all babies go through these changes in their sleep patterns. However, how your baby reacts to these changes will depend on unique factors. Some babies experience a week or two of fussy, interrupted sleep, and then go back to sleeping soundly at night and taking restorative naps. Other babies, however, are thrown all out of whack by the 4 month sleep regression, and they go through weeks and weeks (sometimes even months) of lots of night wakings and missed naps. These babies (and their poor parents!) are hit hard by the 4 month sleep regression, and exhibit a lot of the symptoms mentioned above.

So, if the 4 month sleep regression truly is a bad sleep regression for your baby – how can you cope? Well, we generally advise parents to get to the root of why the 4 month sleep regression is causing such disruptions. Usually, negative sleep associations are to blame – babies who have become accustomed to being rocked or fed or held to sleep continue to need their sleep associations, only now that their sleep patterns have changed, they need them all night long. Of course, mom and dad can’t sustain all that rocking and holding in the middle of the night, and so soon, the whole family is exhausted and overwhelmed. That’s usually when we hear from parents asking for a Personalized Sleep Plan™.

In general, I’d recommend waiting a few weeks, to see if your 4 month old baby’s sleep improves. If it doesn’t, then it may be time to make changes, and to work on weaning your 4 month old from his sleep associations. You might also want to work on establishing a gentle 4 month old baby schedule. I would urge you not to wait indefinitely, though – I talk to parents of 8 month old and even 20 month olds who are still waiting for their “baby” to grow out of their sleep problems.

For more tips on how to cope with and solve your baby’s 4 month sleep regression problems, you can read our other 4 month sleep regression article: The 4 Month Sleep Regression: What It Is and How To Fix It.

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