Sleep regressions and leaps

The terms "sleep regression" and "developmental leap" are extremely common in parenting groups and among sleep consultants. They describe periods when a child's sleep suddenly worsens – often linked to specific ages such as 4, 8 or 12 months. The idea is that the child undergoes a developmental leap that temporarily disrupts sleep.

Do sleep regressions exist?

"Sleep regression" is not a formal medical or scientific standard term. There are no studies that specifically investigate sleep regressions as a phenomenon, and no research confirming that children's sleep worsens in predictable patterns at specific ages. However, there is good research showing that children's sleep varies over time and that periods of worse sleep are common. The distinction matters: the variation is better explained by known factors than by fixed age-specific patterns.

The most discussed sleep regression – at around four months – coincides with a real change in sleep architecture. During the first months, sleep structure matures and becomes more differentiated, with clearer stages of deep sleep.¹ ² However, there is no robust evidence for a universal, predictable worsening at exactly 4 months. Studies that have followed children over time, including a study of 841 children with over 157,000 recorded sleep sessions, suggest that the trend at this age is towards longer consolidated sleep periods at night, with clearer sleep patterns emerging from around 5–6 months.³ ⁴ ⁵ At the same time, some studies show that certain children experience more awakenings during this period, often related to how the child falls asleep and the help they receive upon waking. This maturation is a normal neurological development, not a "regression".

Read more about sleep development →

Leaps – a popular but questioned concept

The idea of predictable mental leaps comes mainly from the book The Wonder Weeks by van de Rijt and Plooij. According to their model, all children go through ten leaps at fixed ages, marked by increased crying and sleep problems.⁶

The original study was based on 15 children.⁶ Some smaller replication studies at universities in the Netherlands, England, Sweden and Spain have been conducted, but with mixed results.⁷ The most well-known independent replication, at the University of Groningen, followed 4 children and found no evidence of increased crying at the ages when leaps are predicted to occur.⁸ Other studies with hundreds of children also show wide individual variation, making it difficult to support a shared timetable for all children.³

Why does sleep seem to come in waves?

Children's sleep varies over time – this is well documented. But the variation is better explained by a combination of known factors than by age-specific regressions or leaps:

• Illness. Colds and ear infections can temporarily disrupt sleep. These periods often coincide with ages associated with "regressions".⁹
• Separation anxiety. Separation anxiety is a normal part of attachment development and can make falling asleep harder and increase night wakings.¹⁰
• Motor development. Periods when the child is learning new motor skills (rolling, crawling, pulling up) are linked to temporarily increased wakings.⁹
• Sleep associations. Many children need help falling asleep and seek the same help during night wakings. This pattern can intensify over time rather than being caused by a specific age.⁹
  Read more about why some children sleep worse →