Of all the sleep regressions, this is the one that doesn't pass
It isn't a step backwards: it's maturation. Your baby's brain changes how it sleeps and doesn't go back — which is why this one doesn't «pass» like the others.
Around four months your baby's sleep stops working the way it used to. It reorganises into adult-style cycles, with light and deep phases alternating all night long. Between cycles there's a brief waking — it happens to all of us, several times a night.
The difference is that an adult falls back asleep without noticing, and a four-month-old doesn't know how yet.
They didn't lose a skill. A new way of sleeping appeared and they can't manage it yet. That's why it isn't a regression, and why sleep doesn't go back to how it was: what has to be built is the new skill.
When it arrives and how long it lasts
It usually starts between day 100 and day 130 of life — not at four months on the dot — and lasts 2 to 6 weeks. If your baby was born prematurely, corrected age is the one that counts.
What you'll see
- More wakings at night, and difficulty settling again.
- Refusing naps they used to take without trouble.
- Needing more help to fall asleep than a month ago.
- Possibly seeming hungrier.
What does help
- Bring bedtime forward by 15 to 30 minutes. Overtiredness makes wakings worse, not fewer.
- More naps, not fewer. Cutting daytime sleep to «tire them out» is what worsens the night most.
- Work on falling asleep in the cot, awake but drowsy: that is exactly the missing skill.
- Steady white noise, which cushions the wakings between light phases.
- More feeds if they seem hungrier.
What doesn't help: waiting for it to «pass». This one doesn't pass on its own, because the change is permanent.
In NomiNest this isn't a table, it's your baby
The app works from the data you already log, and compares your baby against themselves rather than against an average.
Meet NomiNestSources. Ranges are orientative and every baby is different. Based on the infant sleep literature and the stages used by NomiNest's sleep predictor.
NomiNest is not a medical device and this guide does not replace your paediatrician's guidance. The information is general and orientative: every baby is different, and the professional who sees yours is the one who knows them.