Sleep regressions: what research shows

What “sleep regression” means

Parents and guidebooks use “sleep regression” to describe a time when a child who had been sleeping longer stretches wakes more often again, has a harder time falling asleep in the evening or takes shorter naps. Ages often mentioned are 4 months, 8 to 10 months, 12 and 18 months, or two years.

The term comes from parenting books, not from sleep research. The health portal Medical News Today notes that there is hardly any research on the much-cited “4-month sleep regression” and that no study has specifically tested this idea; how common such phases are and how long they last is therefore not known (Medical News Today 2020).

What studies show about sleep development

In a New Zealand study using sleep diaries of 75 babies, the time babies slept at night by themselves in one stretch grew most between the first and fourth month (Henderson 2010). In two large Finnish birth cohorts, sleep quality varied a great deal in the first two years of life; the time to fall asleep became shorter until the sixth month, and night-time sleep consolidated mainly in the second year. Parents’ sleep worries were common at every age there (Paavonen 2020).

An overview of many studies shows how wide the range is: babies and toddlers wake between zero and about three times a night (Galland 2012). A night with several wake-ups is therefore often within the usual range, even if it feels like a step back after a calmer time.

Not every child follows the same curve

An American study followed over 1,200 children from 6 to 36 months. About two thirds were already waking their mothers only about once a week at six months, and that stayed so. The other third still woke their mothers almost every night at six months, on about two nights a week at 15 months and on about one at two years (Weinraub 2012). The researchers speak of two trajectories, not of a right one and a wrong one.

In a Canadian study, at 6 and at 12 months, a good quarter to over half of the babies did not yet have a six- or eight-hour block of sleep. The researchers found no difference in mental or physical development there (Pennestri 2018).

What often falls in the same period

Some changes in sleep coincide with developmental steps. In a small Israeli study of 20 babies, pulling to stand in children who could already do it at about eight months coincided with a period of more restless sleep (Atun-Einy 2016).

Napping changes too: in app data from over 175,000 babies, the number of naps between 3 and 18 months fell on average from almost four to one (Paavonen 2026). In other app data, naps first became shorter between the first and fifth month and then longer again (Mindell 2016). More on this in the articles on nap transitions and short naps.

What expert bodies generally recommend

Expert bodies have no separate recommendations for “sleep regressions”; the general recommendations on children’s sleep apply. The WHO recommends regular sleep and wake-up times for children under five (WHO 2019). In a randomized trial, children with a fixed bedtime routine woke less often and for shorter periods after three weeks (Mindell 2009). Germany’s Federal Institute for Public Health (BIÖG) recommends keeping the light low at night, speaking quietly and not playing.

The BIÖG calls extra help with falling asleep – such as carrying or staying nearby – right in exceptional times such as a new environment. It also describes how children often keep asking for such help once it becomes a habit. How a family handles this is its own decision; Moon Hour does not describe any method.

How Moon Hour handles restless times

Moon Hour learns your child’s rhythm from the last 14 days. Days you mark as special don’t count, so that a few restless days don’t throw off the suggestions. In the history you can see over weeks whether something is changing – this look back often helps more than the impression of a single night.

If you are worried

Experts recommend contacting your paediatrician or your local out-of-hours medical service if you are worried.