Can the 4-month regression be avoided?

No, and it should not be: it is a developmental change. What can be done is not being late for the naps, which is what makes the days worse.

How long does the 4-month sleep regression last?

Two to six weeks of disorder is the usual answer. The new shape of sleep, with more waking between cycles, stays for good.

The 4-month sleep regression: what it is and what it is not

Around four months a baby's sleep reorganises itself: it becomes lighter, with more waking. It is called a regression and the name is a poor one, because nothing goes backwards — it goes towards how they are going to sleep from now on.

What changes underneath

A newborn sleeps in two phases. Around three or four months the phases of adult sleep appear, and with them the wakings between cycles, which did not exist before.

That is maturity, not a problem. What becomes hard is that now, moving from one cycle to the next, they really do wake up, and they have to fall asleep again.

How long it lasts

A few weeks of upheaval and then it settles, though the new shape of sleep is there to stay. The usual bracket runs from fourteen to twenty-three weeks.

During those weeks it is normal for naps to shorten to a single cycle —around 45 minutes— and for wake windows to move about.

What can be done with what you record

Little about the sleep and a lot about the hours. If the naps come out short, the next window is no longer the usual one, and being late for the next nap is what turns an ordinary day into a bad one.

napnap trims the window after a short nap and warns you in good time. It also tells you whether they are staying awake more or less than two weeks ago, which is the figure that settles whether this is the upheaval or simply growing.

Questions

Can the 4-month regression be avoided?: No, and it should not be: it is a developmental change. What can be done is not being late for the naps, which is what makes the days worse.
How long does the 4-month sleep regression last?: Two to six weeks of disorder is the usual answer. The new shape of sleep, with more waking between cycles, stays for good.