top of page

Understanding sleep cycles from birth and beyond.

How newborn sleep changes at 4 months old

As newborns grow older their sleep matures along with their development. Often when they get to around 4 months old sleep can go a bit wonky and often this is due to the maturation of sleep cycles. But what the hell does that mean!?

Let me break it down.

What do newborn sleep cycles look like?

A newborn baby has 2 phases of sleep; quiet sleep and active sleep, they spend about equal time in each of these stages & move between the two.

A baby doesn't have a circadian rhythm or body clock at this stage, so their sleep is not driven by markers such as light and feeding schedules.

A more mature sleep cycle and circadian rhythm develops around the 4-month mark.

So what is a "mature sleep cycle"?!

When a baby moves out of the fourth trimester, they develop a more adult-like sleep cycle. This can mean we see some disruption to the newborn style sleep but that's okay it is often only temporary while they settle into this new pattern.

A circadian rhythm is driven by things like light, feeding times and activity levels, this can mean you can help shape these cycles!

As sleep reaches maturity, a baby now has around a 45-60 minute sleep cycle. As they move from one cycle to the next we can sometimes see disruption to their sleep. Especially if they are sensitive to environmental triggers. You can support them through this by rocking their pram or placing a hand on their chest as they transition into the next cycle.

A full sleep cycle consists of 4 stages:

Non-REM 1:

NEM 1 lasts around 5-10 minutes and is the transition from wake to sleep. This can be a stage that babies experience the startle reflex which wakes them as they move to a new sleep stage. We can help babies to cope better with this reflex through lots of free play on the floor to experience how their limbs move and to allow them to emotionally process this event!

Non-REM 2:

This stage generally lasts around 20 minutes and is often one of the longest part of sleep. During this phase the heartbeat and breathing slows and the body temperature drops. If your child is waking about 25-35 minutes into their sleep consider checking they are cosy enough as this can be an environmental trigger that can cause them to wake up.

Non-REM 3:

N-REM 3 is the deepest sleep state, the body is really relaxed here and there is very little movement. The brain's activity changes to delta waves and the body begins to grow & repair itself. The brain is excellent at managing sleep to ensure you get exactly what you need. When we are ill or have a sleep debt the body will prioritize the deeper sleep it needs to recover!


Also known as "dream sleep", Rapid Eye Movement sleep, is the sleep that we describe as 'active' we may notice changes in babies breathing and fluttering of the eyelids, this is normal! Brain activity increases but the body is in a paralysed state. Breathing and heart rate increase at this stage. This is often where we see older children have nightmares or sleep paralysis. I often recommend a breathing and visualisation exercise where children blow up an imaginary balloon with their bad dream, tie a knot and let it go so it can fly away. This is something my own dad used to do with me and my brother when we were little! If the child is still troubled by their bad dream when they are awake later in the day a worry monster can be a really useful tool to physically write and dispose of nasty dreams. Making the sleep environment feel as cosy and safe is really essential around this time.

Love & Sleepy Dust,

Imogen X

The Little Sleep Company

For more support and advice contact me here!

bottom of page