Around 3-5 months, many babies experience a significant change in sleep patterns. They may have difficulty falling asleep, wake more often during the night, and struggle to return to sleep.
This period can leave parents feeling exhausted and frustrated, wondering why their baby’s sleep habits suddenly changed. Understanding the reasons behind the four month sleep regression can help you cope and support your baby through this stage.
Why the Four Month Sleep Regression Occurs
1. Developmental Leap In The Baby’s Brain
At this age, babies experience rapid cognitive and physical development:
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Cognitive abilities: learning, thinking, reasoning, and memory
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Physical abilities: motor skills and movement
These developmental leaps can temporarily disrupt sleep as the baby’s brain and body process new skills.
2. Changes in The Baby’s Sleep Cycles
Maturing Circadian Rhythm
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The circadian rhythm is an internal biological clock regulating sleep-wake cycles.
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Around 2–3 months, babies begin developing a more regular day-night pattern, which continues to mature around 4 months.
Transition to 4 Stages of Sleep
Newborns start with 2 sleep stages (active sleep & quiet sleep). Around 4 months, sleep reorganizes into 4 stages:
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Stage 1: Light sleep, easily awakened
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Stage 2: First “true sleep,” deeper and more relaxed
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Stage 3: Deep sleep for body repair, growth, and immune development
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Stage 4 (REM): Dreaming and memory consolidation
This transition decreases REM sleep from 50% to 25%, creating more light sleep. Light sleep increases the chances of waking, difficulty falling asleep, and shorter naps, especially if your baby relies on sleep props (nursing, rocking, pacifier).
How to Help Your Baby Adjust
1. Darken the Baby’s Room
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Darkness signals the brain to release melatonin, promoting restful sleep.
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Babies are responsive to light, not afraid of the dark.
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Keep the nursery dark during naps and bedtime.
2. Use a White Noise Machine
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Light sleep makes babies easily startled.
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White noise creates a consistent background, reducing awakenings.
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Place the device at a safe distance and set a safe volume.
3. Maintain a Consistent Bedtime Routine
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Keep routines short (4–5 steps) and predictable.
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Place feeding near the beginning of the routine.
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End with calming activities: warm bath, reading a story, singing a lullaby, pyjamas, and sleeping bag.
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Routine length: 20–30 minutes
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Place baby in the cot awake to encourage independent sleep.
4. Pay Attention to Wake Time
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A 4-month-old’s wake window: ~2 hours
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Bedtime: ideally between 7 PM–8 PM
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Overtired babies struggle to fall asleep and stay asleep
5. Encourage Self-Soothing
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Teach independent sleep by letting your baby nap at least once a day in the cot awake.
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Reduces dependence on nursing, rocking, or pacifiers
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Helps baby connect sleep cycles and sleep longer stretches
Need More Help With Your Baby’s Sleep?
These tips can help your baby sleep better at night and develop healthy sleep habits.
For personalised guidance, book your FREE 20-minute evaluation call today: https://tidycal.com/restedmumhappybub/discovery-call