The Four Month Sleep Regression: What It Is, Why It Happens, and How to Cope

The four month sleep regression, everybody agrees on, and for good reason. It’s the real deal, and it’s permanent.

It is a common phenomenon experienced by many babies and their parents.

At around 4 months of age, babies often go through a significant change in their sleep patterns, causing them to have difficulties falling asleep and staying asleep and wake up more frequently during the night and have difficulties falling back asleep.

As a result, parents may find themselves feeling exhausted and frustrated, wondering what is causing this sudden change in their baby’s sleep habits.

The Four Month Sleep Regression

So, why does the four month sleep regression occur?

1. Developmental Leap In The Baby’s Brain

Their cognitive and physical abilities rapidly progress during this time.

Cognitive abilities refer to a baby’s mental or intellectual capabilities, including their ability to learn, think, reason, and remember.

Physical abilities refer to a baby’s motor skills, including their ability to move their body and manipulate objects.

2. Changes in The Baby’s Sleep Cycles

Baby’s sleep cycles change because of the maturing of their circadian rhythm.

The circadian rhythm is an internal biological clock that regulates the sleep-wake cycle in humans. Before the regression, infants typically have an irregular sleep pattern, with shorter sleep cycles that don’t follow a distinct day-night schedule.

For babies, this process begins to develop around 2-3 months of age, and it plays a significant role in their sleep patterns.

As the circadian rhythm matures, babies start to develop more regular and predictable sleep-wake cycle, with longer periods of sleep at night and more wakeful periods during the day. This process is known as sleep consolidation and is an important milestone in a baby’s sleep development.
Prior to this stage, newborns typically have shorter sleep cycles and spend equal amounts of time in rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. However, as babies mature, their sleep architecture changes and transition from having 2 stages of sleep (active sleep and quiet sleep) to 4 stages of sleep (NREM stages 1, 2, and 3, and REM sleep).

Stage 1: This is the initial stage where it is the lightest stage of sleep. Baby is still somewhat awake and easily aroused.

Stage 2: This is considered the first “true sleep” stage where it is slightly deeper stage of sleep. The baby’s body continues to relax, and brain waves become slower and more synchronised.

Stage 3: This is the deepest stage of sleep, sometimes called slow-wave sleep or delta sleep. During this stage, the baby’s breathing and heart rate slow down even more, and brain waves become very slow and steady. This is where the body starts repairing and rejuvenating the immune system, muscles tissue, energy stores, and sparks growth and development.

Stage 4 (REM Sleep): This is the stage of sleep where the brain starts to kick in and consolidates information and memories from the day before and when most dreaming occurs. During REM sleep, the baby’s brain activity becomes more active, and their breathing and heart rate may become irregular. This stage is also associated with rapid eye movements, hence the name REM sleep.

Once we have gone through all 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 regression we were talking about originally?

Well, newborn babies only have 2 stages of sleep; stage 3 and REM, and they spend about half their sleep in each stage.

But at around the third or fourth month, there is a reorganisation of sleep, as they embrace the 4-stage method of sleep that they will continue to follow for the rest of their lives.

When this change takes place, babies move from 50% REM sleep to 25% in order to make room for those first 2 stages.

So, although REM sleep is light, it is not as light as these 2 new stages that they are getting used to, and with more time spent in lighter sleep, there is more of a chance that babies are going to wake up more frequently during the night, have difficulty falling asleep, or have shorter naps.

And when babies are dependent on a sleep prop (such as being nursed/rocked to sleep or using a pacifier) to fall asleep, they may have a harder time falling back asleep if they wake up during the night or during a nap. This is because they have learned to associate the sleep prop with falling asleep and may not know how to fall asleep on their own without it.

This can lead to a cycle of wake ups and difficulty falling back asleep, which can be frustrating for both the baby and the parents.

So, what can you do to help your little one adjust?

1. Darkening Baby’s Room

Baby’s room should be dark. Newborns and infants are not afraid of the dark. They are, however, responsive to light.

Research has shown that exposure to light can have an impact on sleep quality and duration, and that darkness can help promote more restful sleep. This is because darkness signals to the brain that it is time to sleep and can help promote the release of the hormone melatonin, which is involved in regulating sleep-wake cycles.

While light tells their brains that it is time for activity and alertness, and the brain secretes hormones accordingly, so we want to keep that nursery as dark as possible during naps and bedtime.

2. Use White Noise Machine

With babies 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. White noise can help drown out other sounds and create a consistent background noise that may soothe your baby. Make sure the volume is set to a safe level and place the device away from your baby’s cot.

3. Consistent Bedtime Routine

Bedtime routine is also an essential component to getting your baby sleeping well. Establishing a consistent bedtime routine signal to your baby that it is time to sleep Try to keep the routine to 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 feed-to-sleep association.

So, keep the feed near the beginning of the routine and plan the warm, reading a bedtime story, singing a lullaby, and getting into pyjamas and sleeping bag towards the end. The whole routine should be 20 to 30 minutes long, and baby should be placed in their cot wide awake.

4. Pay Attention to Baby’s Wake Time

Keep their wake time appropriate for their age, which is 2 hours for a 4 month old baby, as overtiredness can make it harder for them to fall asleep and stay asleep. Bedtime should be between 7pm to 8pm.

If your baby is getting fussy before bedtime, it could be a sign that they are kept awake longer that what they can manage and are becoming overtired. A 4 month old baby can only manage wake time of 2 hours before needing to take a nap and bedtime should be between 7pm to 8pm.

5. Encourage Self-Soothing

Teach your baby to self-soothe by placing them in the cot wide awake for at least 1 nap. This helps them learn to fall asleep independently and develop the skills they need to string those sleep cycles together without any need for nursing, rocking, or pacifiers.


Hope these help you and your baby get better sleep at night! Need more help with your family’s sleep? Book your FREE 20-minute evaluation call today.