Sell with Us

Baby Sleep Guide Stage 3 | When Sleep Suddenly Changes - The 4 Month Sleep Regression 

September 26, 2016
Baby Sleep Guide Stage 3 | When Sleep Suddenly Changes - The 4 Month Sleep Regression

The third part from Tinitrader's Safe Sleep series is here covering the 4 Month Sleep Regression and how to fix

Tell me if this sounds familiar: did your 4-month old baby, who was sleeping well at night and taking nice long naps during the day, all of a sudden turn into a sleepless mess?

Gone are the long stretches of sleep between feedings. Gone is the ability to rock or feed him to sleep.

Now, you have an exhausted, fussy baby on your hands – one who won’t fall asleep, let alone stay asleep!!

This is what is often called the 4 month sleep regression.

It’s important to know though, that this is actually not a regression at all but a normal milestone in your baby’s brain development.

During this time your babies sleeping patterns will permanently change and become more like ours.

What Happens When We Sleep

When adults fall asleep, we pass through a series of sleep stages, including light sleep, deep sleep (also knowns as slow wave sleep) and REM (rapid eye movement) sleep.

REM sleep is well-known as our dreaming sleep. It is characterized by a pattern of brain activity, which resembles that of the waking brain.

Although everything below the head becomes temporarily paralysed (in order for us not to act out our dreams!), the eyes dart around beneath the eyelids, and breathing and heart rates become irregular.

For adults, a single sleep cycle - beginning with stage 1 sleep and ending with REM sleep - takes about 90 minutes. At the end of a cycle, we rouse slightly and then fall back asleep again, into the next cycle without even realising it.

How Your Newborn Sleeps in Those Early Weeks

Compared to adults, newborns start life with simple sleep patterns. Babies have two sleep states - active and quiet.

Active sleep comes first.

It's the baby-equivalent of REM sleep, and, like adults in REM, babies engaged in active sleep and can awaken more easily.

yawning bbay

Babies in active sleep exhibit fluttering eyelids; relatively rapid, irregular breathing; body movements; and even grunts or cries.

About half way through the sleep cycle, babies pass from active sleep to quiet sleep.

As its name suggests, quiet sleep is characterized by slower, more rhythmic breathing, little movement, and no eyelid fluttering.

While in quiet sleep, babies are less likely to be awakened by noise and other disturbances.

A baby’s sleep cycle is about 45 minutes in total and if they have a full tummy and nothing else is bothering them, they will enter into another cycle of sleep until they have had enough restorative sleep and wake up.

But Then Everything Changes. EVERYTHING!!

Four months is a very busy time for babies.

Around this time, your baby’s brain matures and her sleeping patterns change – there are now distinctive stages of sleep and they don't drift from one to another so easily.

As sleep becomes more 'adult-like', now when she falls asleep, she does not enter deep sleep right away.

If you have been feeding or rocking to sleep and then try and lay her down before she is in deep sleep, she is more than likely going to wake up and you will have to start all over helping her to fall back to sleep again and again.

baby in bassinet

Initially in the night, your 4 month old will enter deep sleep relatively quickly, within 30 minutes.

However, since a child’s sleep cycle is about 45 minutes, your baby will briefly wake up 45 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.

Given your baby’s deepest sleep is in the early part of the night, you might think that after that first sleep cycle, she might sleep just fine for a few hours.

So, all you have to do is hold her for an hour or so? Nope!

The beginning of the night is your baby’s deepest sleep, and after the first 5 hours, 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 in 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 potentially 1-2 hours).

Between approximately 4 - 6 a.m., is the lightest sleep of the whole night (REM sleep is dominating at this time).

Often parents notice their babies need a “nap” soon after “waking up”. Be careful not to mistake a night waking from difficulty sleeping at this time from starting the day!

Why Are Sleep Associations So Important?

The way we put our babies down to sleep as well as the way we resettle them during naps or in the night will dictate how they learn to go to sleep.

We call these things “sleep associations”; cues or behaviours your baby associates with going to sleep.

Sleep associations are a normal part of falling asleep.

Even as adults we need something to help us fall asleep (think a pillow and blankets).

It's when these associations disrupt your baby's sleep, because they require your assistance, that it becomes a problem.

swaddle your bub

If a baby relies on a parent-controlled sleep association to fall asleep at the start of a nap or at bedtime, they will then need the same conditions replicated when they surface from their sleep cycles during the day and in the night.

What Can I Do?

You might be thinking by now that because you started one way (by always feeding or rocking to sleep) that this is the only way that your baby will always need to sleep.

This is definitely not the case!

When these things stop working, you just need to switch it up and find something new to help teach your baby how to get the sleep they need.


  • Make sure you have age appropriate expectations for how much and when your baby should be sleeping by this age.

  • Determine what sleep associations your baby has to determine the ones you want to work on changing

  • This is a good age to start practicing putting your baby down in their cot drowsy but awake. They may need some cot rocking or patting in their cot to help with this transition.

  • Teach your baby to self-soothe by allowing them the opportunity to learn how to do it and by making them as comfortable as they can be alone

  • Give your baby time to settle himself. The temptation, especially with our first baby, is to jump in and soothe him as soon as we hear the first squawk. Instead, let your baby have a few seconds to settle or find a strategy himself. This doesn’t mean leaving your baby to cry, it simply means that you take a deep breath and listen to his communications. If he’s groaning and moaning, leave him to settle. If he’s really crying, respond and find out why.

hand sleeping

Kate has worked in the field of Sleep Medicine for over 15 years. She has a Ph.D. from the University of Melbourne and has since worked extensively both here in Australia as well as most recently in the Division of Sleep Medicine at Harvard Medical School and Brigham and Women’s Hospital. She is passionate about working with families to help children sleep better and is the founder of Babysomnia. She currently lives in Melbourne with her husband and four young children. If you have a question for Kate you can ask it on the Facebook page or for more information check out the website at

Read our Email and Privacy Policy