by Anya Dunham, PhD
The 4 month baby sleep regression: why it happens, 2 things to do, and 2 things not to do.
You might have heard about – or, perhaps, are in the trenches of - the 4 month baby sleep regression.
Many families say that their previously good sleeper began waking a lot at night and struggling with naps around 4 months. Approximately 9% of babies have a very hard time sleeping at this age; some of these babies had colic and some did not.1 Many other babies still sleep fairly well, but wake up more than they did before. What is going on?
Young babies often sleep quite a bit and go to sleep easily, because their homeostatic drive — also called sleep pressure2 — builds quickly, and they sleep for as long as they are tired. But now, at around 4 months old, your baby is developing distinct sleep cycles and tends to wake up briefly after each period of light REM sleep. (See those peaks into "awake" and "REM sleep" in the chart below? More details here.)
Once a baby develops distinct sleep cycles and consolidates most of her sleep into nighttime — usually by 4 months and almost always by 6 months — her sleep biology will remain fairly constant throughout her life.2,3 This is a progression rather than a regression. (I think of it as a sleep shift.)
There are many developmental leaps happening around this age: your baby is learning to roll, grasp, and use her voice in different ways; she’s figuring out patterns in the world around her and growing fast. She is working hard and may need extra time to wind down.
When a baby does not get the rest she needs in the early weeks, overtiredness may catch up to her around the 4-month mark. She may have been going to bed too late, napping during car rides, or staying awake too long between naps. As she moves to three naps a day, she may become overtired and her sleep may get disorganized.
If you feel your baby is overtired, think about how you can offer her more sleep. Can you move her bedtime to an earlier hour or shorten her wake times? Might your baby be getting overstimulated when she’s awake and, because of that, having a harder time winding down? Can you make changes to her sleeping space to make it more conducive to sleep (for example, darker, quieter, or cooler)? Can you offer your baby the last nap of the day in a baby carrier if your baby sleeps well that way?
Even if your baby is well-rested, he’s still going through the sleep shift and developmental leaps. To help him navigate this phase, continue keeping him well-rested with the comfort of familiar routines. This might be the time to do fewer outings and baby activities – for a little while.
The term “self-soothing” may sound negative, as it seems to imply that instead of actively comforting an upset baby, the parent leaves the baby to his own devices. I wholeheartedly agree that babies should not be left to “self-soothe” from a place of distress. However, a baby who woke between sleep cycles may be tired, but not necessarily in distress or even upset.
Many babies make at least brief attempts to calmly return to sleep on their own when they wake up when they are as young as 1 month old.4,5 (This is one reason why I prefer the term "self-settling".)
Give your baby opportunities to experience what it feels like to go to sleep on her own when opportunities present themselves. (Here is how we did it.)
Many sleep experts recommend starting some form of sleep training around this age, which usually involves cutting out at least some nighttime feeds. I don’t agree with this approach.
Continue feeding your baby when he’s hungry. Don’t introduce solid foods before 4 months in hopes of getting more sleep. Remember, your baby doesn’t wake up because he’s hungry; rather, he wakes up naturally between sleep cycles.
(Here are 4 signs your baby is ready for solids – none of them have to do with night wakings...)
Resist reverting to the late bedtime your baby had when she was younger. Sometimes parents go back to a late bedtime because their baby seemed to sleep better that way. The thing is, it’s the adults who were getting more sleep: the long stretch of baby’s sleep — the first one after baby goes to bed — used to overlap with theirs. But babies who go to bed late tend to get less sleep overall6,7 and can become overtired, which eventually leads to less sleep for the whole family.
I cover the 4-month sleep regression (and other sleep challenges) in more detail in my book, Baby Ecology.