The general consensus among sleep specialists is that there are roughly six stages of sleep regression at different ages: when the baby is 4 months, 6 months, 8 months, 12 months, 18 months, and 2 years old.

Typically, these regressions are associated with the various developmental milestones a baby experiences around those ages, such as learning to sit up, crawl, and walk. Other causes include separation anxiety, big life changes, and a desire for independence.

However, there is not much published research on infant sleep regressions.

This article explains the stages and causes of sleep regressions, as well as other reasons a baby may experience sleep disturbances.

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The term “sleep regression” refers to a period of time when a baby or toddler experiences a shift in their sleeping pattern.

Often, sleep regression signs include:

  • fighting naps or bedtime
  • difficulty falling asleep
  • taking shorter naps or skipping naps
  • frequently waking at night
  • fussing and crying

There is not much current and formal research on infant sleep regressions. However, some older research suggests regressions are responses to the developmental changes babies experience during the first couple years of life.

For example, an older study from 1991 suggests that periods of change in sleep patterns and behavior often coincide. Likewise, a 2002 case report found that sleep regressions may happen alongside the developmental brain changes that happen roughly between 2 and 21 months of age.

That said, it seems sleep regressions may happen for various reasons, including:

  • developmental milestones (learning to crawl, walk, talk)
  • needing to transition to one nap per day
  • separation anxiety
  • growing desire for independence
  • life changes (potty training, moving from crib to bed, getting a sibling)

However, sometimes, what looks like a sleep regression is actually more of a sleep disruption due to growing pains, teething, hunger, and reflux. Additionally, a baby may have trouble falling and staying asleep because they have not established solid sleeping habits.

Like most things regarding babies and toddlers, sleep regressions can vary in when they happen and how long they last.

However, many specialists seem to agree the most common regressions happen around 4 months, 6 months, 8 months, 12 months, 18 months, and 2 years of age and last between 2 and 6 weeks.

4-month sleep regression

Typically, the 4-month sleep regression is the first sleep pattern change babies experience.

However, not all babies experience it. For those who do, it might come a month or so earlier or later.

Signs include:

  • changes in nap routines
  • waking more frequently at night
  • restless sleep
  • trouble falling back asleep

Generally speaking, the 4-month sleep regression is less of a regression and more the beginning of a permanent change in a baby’s sleep pattern. Around this time, babies start sleeping more like adults and less like infants, so this “regression” is typically like a springboard into more mature sleeping patterns.

Learn more about the 4-month sleep regression timeline here.

6-month sleep regression

There is some debate about the 6-month sleep regression, specifically as to whether it actually exists.

Some argue that sleep disturbances around this age do not last long enough to qualify as a true sleep regression.

Generally, babies around this age wake at night because they are hungry. Maybe they are breastfed and still need a night feeding, or maybe they need to replenish the calories they burned during the day practicing their scooting, crawling, and sitting up skills.

On the other hand, some claim the 6-month sleep regression is a true regression, though they admit it is a short-lived one. Additionally, these advisors add newfound skills, teething, and separation anxiety to the list of causes.

Regardless of phrasing or reasoning, the signs are the same: waking at night, fussiness, and longer daytime naps.

8-month sleep regression

This stage is also called the 8- to 10-month sleep regression because it may happen any time during that age range.

As with most sleep regressions, this one seems to coincide with developmental changes such as learning to pull themselves to a standing position or crawl.

Also, some babies get their central incisor teeth between 8 and 12 months, which may contribute to this sleeplessness. Anyone concerned about teething may ask a pediatrician for advice.

Learn more about the 8-month sleep regression here.

12-month sleep regression

There is not much mystery surrounding the 12-month sleep regression. For some babies, it might happen as early as 11 months, or blend in with an 11-month regression. For some babies it might not even happen at all.

Similar to most sleep regressions, the 12-month sleep regression seems to happen due to the baby’s growing skills, and awareness of the world around them.

Caregivers keep babies on a regular bedtime routine, to help this regression pass.

18-month sleep regression

It is safe to say toddlers go through many changes around the middle of their second year, and some of those changes contribute to the 18-month sleep regression.

One change relates to the toddler’s circadian rhythms — more specifically, the 24-hour sleep-wake cycle.

Babies begin establishing a sleep-wake cycle during the first 4 months of life. However, rapid eye movement (REM) and non-rapid eye movement (NREM) change over a person’s lifetime, including the first 5 years of life.

This may cause some toddlers to start fighting their usual bedtime. Both REM and NREM are sleep phases that are important for various mental and physical processes.

Additionally, some toddlers go through the 18-month sleep regression because they are dealing with separation anxiety and do not want to be away from their caregivers.

At the same time, toddlers around this age begin wanting more independence. They want to stay awake so they can practice their growing skills and explore the world around them.

Learn more about the 18-month sleep regression causes, management tips, and self-care for adults.

2-year sleep regression

Typically, the 2-year sleep regression is the last one.

Causes may include:

  • life changes such as potty training or moving to a toddler bed
  • return of separation anxiety
  • night terrors, nightmares, and nighttime fear (think “monster under the bed”)

There are a few ways caregivers can help ease this regression, including:

  • initiating one life change at a time (e.g. toddler bed and then potty training, or vice versa)
  • increasing wake time between the afternoon nap and bedtime
  • teaching skills to cope with nighttime fear

Additionally, the toddler may experience a nap regression.

Generally, toddlers this age take an afternoon nap. Some may start resisting this nap, confusing caregivers into thinking they are ready to stop napping. However, typically the afternoon nap lasts through and sometimes beyond toddlerhood, and caregivers may treat this resistance as a regression.

A sleep regression is an abrupt change in an infant’s sleeping pattern, and many babies experience several stages of sleep regression during the first 2 years of life.

Typically, these sleep regressions are connected to the baby’s developmental changes, though other factors, such as teething, can influence shifts in their sleeping habits.

For the most part, sleep regressions stop after around the 2-year mark.