The 4-month change, and why it isn't a setback

Around four months, sleep stops being newborn sleep. It gets lighter, more cycled, more like yours - and the nights that had started to settle come apart. That isn’t a regression. It’s a rebuild.

4 min read

For the first few months, babies drop straight into deep sleep and stay there. Then the architecture changes: sleep splits into cycles, and between cycles there’s a surfacing - a brief, almost-awake moment. Adults have these too. You turn over and never remember it.

A baby who has always fallen asleep one particular way will surface and look for that way again. If it was motion, they want motion. If it was a feed, they want the feed. Nothing has broken. They’ve simply started noticing the gap.

What to hold steady

The instinct is to change everything at once - earlier bedtime, longer naps, a new settling method, a different room. Change one thing and give it four nights. Two nights tells you almost nothing; a week is longer than most parents can hold their nerve.

Nothing has gone backwards. The thing that used to work stopped being invisible.

The naps go too, and that is expected

The same change shows up in the day, usually as naps collapsing to thirty or forty minutes - one cycle, and then awake. This is the most common complaint at four months and it is the least worth fighting. Extending naps at this age is unreliable work; bringing bedtime forward on the days they are short is far more effective and much less exhausting.

Wake windows are lengthening at the same time, to roughly an hour and a half to two and a half hours. A window that fitted perfectly a fortnight ago may now be leaving your baby short of pressure at nap time, which produces exactly the short naps you are trying to fix.

How long it usually takes

Most families see the nights steady over two to four weeks, and it rarely happens in a straight line - a good stretch, then two rough nights, then a better week. Some babies take longer. Nobody can put a date on it, and anyone who does is guessing.

One thing worth being clear about: this is not the moment to reduce night feeds. Hunger genuinely increases around four months, and a baby waking more often at this age is frequently waking for a real reason as well as an architectural one.

What is worth changing while it happens

One thing, and it is not a method. If your baby has always arrived in the cot already asleep, the useful change is to start putting them down while they are still just awake - at bedtime, once a day, with you staying beside them. Some nights it works and some nights you pick them up and do it the old way.

That is the change that addresses the actual mechanism, because it alters what your baby finds when they surface. Everything else on offer at four months - dropping feeds, extending naps, timed checks - either works against the developmental grain or fixes something that is not broken. Slow, unglamorous, and it is the one that pays.

What not to try this month

Dropping night feeds, which is the opposite of what is needed - hunger genuinely increases around four months. Extended-separation settling methods, which are not appropriate at this age. And a full restructure of the day, which changes so many variables at once that you learn nothing from any of them.

Starting solids to fix it belongs on the same list. There is no good evidence it improves sleep, current guidance is around six months anyway, and in the short term it more often disturbs nights than settles them.

When to stop troubleshooting

If feeding is painful, if there’s a lot of arching or refusing, if there is snoring or noisy breathing during sleep, or if something just feels off to you, that’s a conversation with your health visitor or paediatrician rather than a sleep problem to schedule around.

General guidance, not medical advice. Your paediatrician's advice takes precedence.