The 4-Month Sleep Regression
Why your baby stopped sleeping well — and what to do.
At 4 months, your baby's brain matures and their sleep architecture changes permanently, becoming similar to an adult's: cycles of light and deep sleep alternating. This is permanent — it's not a phase that "just passes." But you can help the process.
This is a permanent neurological change. Your baby now has shorter sleep cycles (~45 min) and wakes between cycles. The goal isn't to return to the newborn who slept 3 hours straight, but to help them chain cycles together.
Key facts
Age
3.5-5 months
Duration
2-6 weeks
Normal cycle
~45 minutes
Night wakings
4-6 normal
How to support sleep
Consistent routine: same sequence every night (bath → massage → feed → song → crib)
Sleep window: max 1.5-2 hours awake between naps at 4 months
Try to put down when sleepy but still conscious
Constant white noise — mimics the sound of the womb
Dark room: blackout curtains make an enormous difference
Always on their back to sleep, on a firm flat surface, without pillows, loose blankets, or positioners. This reduces the risk of SIDS. (AAP Safe Sleep Guidelines 2022)
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The 4-month sleep regression doesn't resolve on its own — but it's manageable with a consistent routine.
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Track your baby's sleep in mi·ma and identify their exact sleep windows. We alert you when the regression approaches so you're prepared.
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mi·ma is a support logbook for parents. This guide is informational and does not replace consultation with your pediatrician. For any concerns about your baby's health, consult a healthcare professional.
Sources
- · AAP Safe Sleep Guidelines 2022
- · Healthy Sleep Habits, Happy Child (Weissbluth, 2015)