The 4-Month Sleep Regression: What It is and What to Do About It

You may have heard of the 4-month sleep regression and dreaded the thought of your baby going through it. The truth is, this is a maturation of development and sleep. It can feel challenging but is a good sign that your baby’s body will soon be ready to sleep in more regular patterns.

The 4-Month Sleep Regression

Most babies go through the 4-month sleep regression between 3 and 5 months. You will often notice signs of the changes around 3-3.5 months, and by 5 months, you can work on a more solid schedule, and sleep can be balanced out if this is your goal.

What is happening during this sleep shift?

Newborn Sleep

Newborn sleep is simple, with two distinct stages of sleep. REM Sleep is also called “active” sleep, and Non-REM sleep is also called “quiet” sleep. REM (active) sleep is when you may notice them twitching, breathing irregularly, smiling, and when you see their eyes moving beneath their eyelids. Non-REM (quiet) sleep is when your baby is breathing deeply and lying very still.

4 Month Sleep Shift

During the sleep regression, many changes begin to occur in the body:

Your baby is producing more Melatonin! Melatonin is our sleep hormone that tells the body when it is sleep time. Before this change, your baby’s physical needs more so determined their wake/sleep cycle.
Non-REM sleep is further dividing. There are now four stages and some periods of “deep” sleep are lighter than others.
Partial awakenings occur during the sleep cycles. These awakenings generally happen once a sleep cycle and serve the purpose of protecting our baby (we have them too!). Your baby comes out of sleep to assess their surroundings and ensure that they are safe and their needs are met.

These awakenings are a primary factor in sleep disruptions. Before this developmental milestone, your baby usually woke for a physical need of feeding, diaper change, or comfort. But now, they are experiencing these awakenings even if they don’t need anything. This is where babies begin to form associations for sleep. Cues present when your baby falls asleep become a cue for sleep in the brain. When your baby comes into a partial awakening and does not have a physical need, their body will need the cue to go back to sleep. Once your baby goes through this maturation, you may notice that they have more night wakings, shorter naps, and it can be harder to put them to sleep. This is what I refer to as a negative association. It is NOT “bad,” but it interrupts sleep.

Matured Sleep

Following the sleep shift, your baby’s sleep pattern will now be similar to your own. Sleep cycles will lengthen as they get older, and you will see a natural shift to more night sleep and less daytime sleep through nap transitions and longer awake times. However, partial awakenings are still part of the sleep cycle, and cues for sleep can get stronger. This is often when families notice that their baby frequently wakes at night and takes short naps even though the sleep regression has passed. Working on the cues that your baby uses at the beginning of the night to fall asleep can greatly improve night wakings because your baby will have new strategies on how to go back to sleep during the awakenings if they do not have a physical need such as a feed.

How to get through the sleep shift/regression.

Use appropriate awake times between sleep periods. For example, an overtired baby and a baby who is not tired enough can wake more frequently and/or take short naps.
Follow wake windows to allow for an early bedtime. For example, a bedtime between 6 and 8 p.m. is normal around the 5-6 months following the sleep shift.
Have the last nap of the day ending by 5:30 p.m. This sets up a nice bedtime.
Set up the room environment to help sleep cycles flow and sleep hormones produce.
Focus on consistent routines. Routines are your baby’s clock and help signal the brain to produce sleep hormones and prepare for sleep.
Be patient! The shift can take time, and I truly believe that month 3 to month 4 is the hardest in terms of sleep. Your baby is not ready for sleep strategies until 16 weeks of age, yet the maturation of those sleep cycles is kicking your butts.