4-month regression playbook
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4-month regression playbook.
It's not a regression — it's permanent maturation of sleep architecture. Mature cycles + new wake-window length = the disruption you're seeing. Here's what to do, what to avoid, and the timeline.
Until ~4 months, babies sleep in 2 stages (active + quiet). Now they shift to 4 stages including REM and deep NREM — adult-style sleep architecture. They surface briefly at the end of each sleep cycle (shorter than an adult’s at this age) and have to learn to resettle without help.
2-6 weeks for most. The architecture change is permanent; the disruption is temporary. By 5-5.5 months, babies who’ve learned to link cycles independently sleep longer stretches than they did before the regression.
| Mistake | Why it backfires | Do this instead |
|---|---|---|
| Adding a feed at every wake | Reinforces feed-to-sleep association at exactly the moment baby is learning to link cycles independently. Feed becomes the only resettle tool. | Feed when baby is hungry (ask your pediatrician if you’re unsure how many night feeds your baby still needs). At other wakes, try brief presence + pat-shush first. |
| Earlier bedtime to “catch them up” | Bedtime is already approximately right. Earlier = waking earlier in the morning, which fragments the night further. | Hold bedtime steady. If overtired, bring it 15 min earlier — not 60. |
| Bringing baby to your bed | Hard to undo once started; AAP advises against bed-sharing with infants under 12 months for SIDS reasons. | Pull crib into your room (room-sharing is recommended for at least the first 6 months) — gives proximity without the safety risk. |
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