The 4-month sleep regression: what it is and how to get through it

At 4 months, your baby who used to sleep 6 hours straight suddenly starts waking every 2 hours. You haven't done anything wrong — it's pure biology.

What happens at 4 months

Your baby's brain is going through the biggest reorganization since birth. Sleep cycles mature from 2 phases (newborn) to 4 phases (adult). Between each 40-minute cycle, the baby partially wakes — and if they don't know how to fall back asleep on their own, they cry.

How long it lasts

2-6 weeks on average. Some babies move through it in 10 days, others need 8 weeks. It's not something you "fix" — it's something you go through.

What works

• Absolute consistency with the bedtime routine — even when it doesn't seem to be working
• Put baby in the crib drowsy but awake — this is THE moment to learn self-soothing
• Don't introduce new habits (nursing to sleep, rocking) that you'll have to undo later
• Make sure there's enough daytime sleep — an overtired baby sleeps WORSE at night
• Use white noise — it masks sounds that could wake the baby between cycles

How Lulla helps

By tracking with Lulla, you'll see exactly how things evolve. The Sleep Score will dip temporarily — that's normal. But you'll spot the recovery pattern and have concrete data for your pediatrician if needed.