Understanding the Science Behind Baby Sleep

Why Is My Baby Not Sleeping Well?

If there's one recurring topic among parents in my clinic, it's sleep.

"My baby wakes every hour."

"She only naps for 30 minutes."

"He will only sleep if I carry him."

These concerns are incredibly common. The good news is that most infant sleep challenges are explained by normal brain development rather than something being "wrong."

Understanding how sleep works helps parents set realistic expectations and develop healthy sleep habits that improve over time.

Sleep Is Essential for Growth

Sleep is one of the busiest times for a baby's brain.

During sleep:

• Growth hormone is released.

• New memories are stored.

• Brain connections strengthen.

• The immune system develops.

• Emotional regulation improves.

  
  

This is why infants spend so much of their first year asleep.

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Babies Are Not Mini Adults

Babies are born with an immature sleep system.

Unlike adults, they have:

• Short sleep cycles

• No established body clock

• Tiny stomachs requiring frequent feeds

• Immature nervous systems

• Rapidly developing brains

  
  

Adults usually sleep for around 90 minutes before briefly waking, rolling over and drifting back to sleep without even remembering it.

Babies do exactly the same thing—but they haven't yet learned how to settle themselves back to sleep. Newborn sleep cycles are much shorter, lasting only about 40–50 minutes. That means they have many more opportunities to wake during the night.

As babies grow, these sleep cycles gradually become longer and more mature.

The Three Stages of Sleep

Sleep isn't one long, uninterrupted period. It consists of repeating cycles made up of light sleep, deep sleep and REM (Rapid Eye Movement) sleep.

Light Sleep (non-REM Stage 1 & 2)

This is the easiest stage to wake from.

During Stage 1, baby appears drowsy with heavy eyes, progressing into Stage 2 when baby is disengaged from surroundings but may easily startle.

Deep Sleep (non-REM Stage 3 & 4)

The body repairs itself, growth hormone is released, immune system is strengthened and bone growth occurs.

It is hard to wake baby up from deep sleep.

REM Sleep

REM sleep is where much of the brain's learning and memory consolidation occurs.

This is a light but active sleep, when dreaming occurs.

REM sleep becomes longer as the night progresses, hence we spend more time in light sleep as morning approaches.

Newborns spend almost half of their sleep in REM compared with around one-quarter in adults.

How Sleep Changes from Birth to Toddlerhood

Newborn (0–3 months)

Newborns usually sleep 14–17 hours in 24 hours, but in short bursts.

Their sleep cycles last only 40–50 minutes, and they wake frequently because their tiny stomachs need regular feeding.

At this stage, there is poor day/night differentiation as baby lacks melatonin (sleep hormone).

Frequent waking is completely normal.

3–6 Months

Around 3 months of age, babies begin producing their own melatonin and develop an internal body clock (circadian rhythm).

Night sleep gradually becomes longer and more organised, while daytime naps become more predictable.

6–12 Months

Sleep cycles lengthen to around 60 minutes.

Babies naturally wake briefly between sleep cycles. Some settle themselves back to sleep, while others need help returning to sleep.

This is often the stage when parents notice frequent night waking.

Toddlers

By toddlerhood, sleep cycles resemble those of adults and last approximately 90 minutes.

Most toddlers require 11–14 hours of total sleep daily, including one daytime nap.

Melatonin: The Body's Night-Time Signal

Around 2–3 months old, babies begin producing their own melatonin. Melatonin is our body's sleep hormone that helps us settle into sleep, and peaks between 6.30pm to 8pm. Darkness at night triggers melatonin production and helps to regulate our internal body clock (Circadian Rhythm).

Parents can encourage healthy melatonin production by:

• Plenty of morning sunlight

• Bright daytime activity

• Dim lights after sunset

• Avoiding screens before bed

• Calm overnight interactions

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Why Do Babies Wake Between Sleep Cycles?

It is perfectly normal for everyone—adults included—to wake briefly between sleep cycles.

Most adults do not remember these awakenings because they quickly return to sleep.

Babies, however, are still learning this skill.

If a baby falls asleep while being:

• Rocked

• Fed

• Held

• Nursed

• Pushed in a stroller

they may expect the same conditions when they briefly wake between sleep cycles.

If those conditions have changed, they may fully awaken and signal for help.

These are sleep associations that many babies develop.

Self-Soothing and Connecting Sleep Cycles

As babies mature neurologically, they gradually learn to settle themselves back to sleep.

This process is sometimes called self-soothing.

Self-soothing does not mean leaving a baby to cry unattended. Rather, it refers to developing the ability to fall asleep with less external assistance.

When babies learn to settle independently at bedtime, they are often better able to reconnect their sleep cycles, and sleep in longer stretches at night.

Like walking or talking, this is a developmental skill that develops gradually and at different ages for different children.

Why does my baby not sleep well?

While dependency of sleep associations and inability to self-soothe to sleep is a common cause of poor sleep, there can be many other reasons:

• Inconsistent bedtime routine

• Poor sleep schedule including naps

• Overtiredness

• Concurrent developmental milestones

• Hunger/discomfort

• Suboptimal sleep environment

  
  

Every Baby Is Different

Some babies naturally sleep long stretches from an early age, while others continue waking overnight well into toddlerhood.

Sleep is influenced by age, temperament, feeding, illness, developmental milestones and family routines.

There is no perfect sleeper.

The goal is not to eliminate every night waking, but to build healthy sleep habits that support your child's development and your family's wellbeing.

The Bottom Line

Healthy sleep is a journey rather than a destination.

Understanding the science behind sleep cycles, melatonin and healthy sleep habits helps parents respond to sleep challenges with realistic expectations and confidence.

With patience, consistency and gentle support, most children gradually develop healthy sleep habits over time.

In the next article, we'll explore one of the most misunderstood aspects of infant sleep: wake windows.