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The 4 Month Sleep Regression and why your baby won't sleep

four month old baby struggling to fall asleep
Understanding WHY your baby has suddenly stopped sleeping can help you get through this phase.

Picture this...

Your baby is a few months old, and you have finally gotten a few hours of undisturbed sleep. Maybe you have a nice little routine going. You have figured out some of your baby's sleep cues and have some sure fire ways to soothe them. You’re thinking to yourself “I think I have a handle on this sleep thing!”

Then BOOM!

Around that 3-4 month mark, your baby suddenly starts waking up shortly after going to sleep and waking multiple times per night.

Will not nap. No. Matter. What. You. Do.

What is going on?!

Your baby might be entering the 4 month sleep regression.

Like all sleep regressions/progressions, the 4 month sleep regression is rooted in developmental changes. In addition, your baby’s sleep cycles change dramatically, making it harder for them to settle and maintain longer periods of sleep.

Your baby's sleep cycles mature around the four month mark

Most people know of two different sleep cycles. REM sleep (rapid eye movement, when we dream) and NREM (non rapid eye movement, or deep sleep). In children and adults over 4 months, NREM sleep is broken into four stages:

  • NREM 1: Lightest sleep, right after drifting off. You are easily awoken during this stage.

  • NREM 2: Lighter sleep. You are a little more asleep, but sleep is still easily disrupted. You may experience, hypnic jerks during this phase.

  • NREM 3: Deep sleep. Restorative cell growth and growth hormone are released.

  • NREM 4: Deepest sleep. Very hard to rouse, parasomnias may occur.

During the first few months of life, your baby experiences a distinct sleep pattern characterized by transitions between REM (rapid eye movement) sleep and NREM3 (deep sleep). This pattern typically looks like:


However, around the fourth month, your baby's sleep cycles begin to resemble those of an adult more closely. This shift involves a pattern of:

  • NREM1 – NREM2 – NREM3/4 – NREM2 – NREM1 – REM sleep

Light sleep and increased wakefulness

This means your baby is literally experiencing “falling asleep” for the first time. As they enter NREM 1/2 they wake more easily upon transfer to their crib. As they cycle through NREM 1/2 throughout the night, they are easily roused and more likely to signal to you, especially if they have a need for a feed/diaper change or comfort. This increase in light sleep also leads to shorter naps which are very normal in months 3-5 of your baby’s life. Although these sleep disruptions are super hard on us as parents, it’s important to remember they are likely temporary and a result of your baby's developing sleep architecture.

Increased Awareness and Sensory Stimulation

On top of your baby’s sleep cycles maturing, as the fourth trimester comes to an end, your baby becomes more aware of their surroundings. Everything becomes brighter, louder, and their brain is actively forming millions of neural connections. While this newfound awareness is exciting, it can also impact your baby's sleep. Falling asleep now means being separate from their favorite person (you) and their safest place (your embrace).

Tips to navigate the 4 month sleep regression

Establish a Consistent Bedtime Routine

A predictable bedtime routine signals to your baby that it's time to wind down and prepares them for sleep. Incorporate soothing activities such as a warm bath, gentle massage, or lullabies to create a calm atmosphere.

Create a Sleep-Friendly Environment

Ensure that your baby's sleep environment is comfortable, quiet, and dimly lit. Consider using white noise or a soft nightlight to create a soothing ambiance that supports sleep.

Embrace Naps

Shorter naps are common during this phase, but it's essential to provide your baby with opportunities for daytime sleep. Encourage regular nap times and provide a conducive sleep environment to help them settle and establish a healthy sleep routine. Do not worry too much about where your baby is sleeping. It is better for your baby to get the sleep they night and prevent overtiredness, then obsess about getting them to sleep in their crib or bassinet.

Respond to Your Baby's Needs

During this time, your baby may require additional comfort and reassurance. Be responsive to their needs and offer soothing techniques such as gentle rocking, shushing, or cuddling when they wake up during the night.

There is no way to sugar coat it, the fourth-month sleep regression can be a challenging phase for both babies and parents. Understanding the changes in your baby's sleep patterns and providing a supportive sleep environment can help ease the transition. Remember, this phase is temporary, and with time and consistency, your baby's sleep patterns will stabilize. Be patient, flexible, and remember that baby sleep is not linear. Before you know it, you'll be through it and onto the next exciting phase of your baby's development.

Looking for more ways to support your little one's sleep without Cry it Out? Check out our freebie guide SHAME FREE 6 MONTH SLEEP SOLUTIONS here



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