The science of baby sleep

How it changes, and what’s really ‘normal’

Sleep! It’s the biggest part of any new parent’s life, and yet there seems to be nothing but conflicting advice out there. Why? Well, mostly because researchers yet say what the ‘right’ way is to help a baby sleep – or even if there is one. It means that most baby-sleep tips are based on guesswork, anecdotal evidence or cultural norms. 

In this article we’ll explore what science does know about infant sleep, to help you more successfully navigate all that advice and find what works for you.

How your baby’s sleep changes

The one thing we know is that all people – and therefore all babies – are different. It means that there is no one-size-fits-all chart or approach. Below we’ve outlined what research tells us are the averages, which could – along with getting to know your baby – help you understand how best to approach sleep.

0-3 months

Newborns sleep whenever, wherever – 10 minutes at a time, or up to five hours. There’s no way to predict it. This is because they’re born without a circadian rhythm – the internal clock that makes us sleepy after dark and more awake in the day.

Before birth their sleep is regulated by their mother’s melatonin production – the hormone that creates the sleepy feeling. After birth, newborns must develop their own circadian rhythms – most infants take about 12 weeks to show day-night rhythms in their melatonin production.

3-4 months

Baby sleep patterns are becoming more adult-like – this is often the cause of the dreaded four-month sleep regression. Your baby used to plunge straight into the REM (rapid eye movement) phase of sleep. Now they have a period of light sleep (like adults) then deepen into slow-wave, deep sleep phases.

It’s about now that their circadian rhythm comes into full force – their wake-up hormone, cortisol, begins to complement their sleepy melatonin production. Around 50% of parents report their baby was sleeping for five hours or more at this age.
Your baby is still napping all day, and will sleep for between 12-16 hours all up.

5-6 months

At this age, most parents find their babies sleep for at least five hours overnight, and some for as long as ten hours. But it’s totally normal for your baby to be waking up three to four times overnight.

Your baby is still likely to be taking several naps during the day, and may be showing some signs of a pattern – waking and napping at similar times each day. On average, your baby will still be sleeping between 12-16 hours.

7-12 months

Is your baby still not sleeping in a five-hour block overnight? Don’t worry – it’s totally normal. One study suggests that 15% of 12 month old babies still weren’t either! 

If you’re sleeping better, it’s not because your baby has stopped waking. They’re probably still waking 3-4 times a night, but at this stage many babies can fall back asleep on their own – they don’t need you, so you can stay in bed!

Your baby will be napping less during the day but they’ll be sleeping about the same amount in total – between 12-16 hours a day.

Sleep regressions are actually signs of progress

Sleep regressions are periods where, seemingly out of the blue, babies wake more and take longer to fall asleep.

They’re most often caused by developmental bursts – ones you can’t see in newborns, but are obvious in older babies (Walking! Talking!). For example, a recent study shows that when babies learn to crawl they have a harder time sleeping at night – something most parents can tell you is true! Researchers suspect this is down to either the baby being excited by their new skill, or because the change needed to make that developmental leap also messes with sleep-wake cycles.
In this way, it might not be that helpful to label these times as ‘regressions’ – they’re anything but!

Here are some of the common ‘sleep regressions’ and what scientists think might cause them. These are all just approximates and averages. Most babies develop very well on their own time scale, and there is a very wide range of normal – so there’s likely no need to worry if your child doesn’t quite fit into the averages.

6 weeks

These times are almost certainly due to growth spurts and burgeoning awareness.

3-4 months

This can be one of the hardest to navigate. On top of their speedy growth and bursts of brain development, babies’ sleep patterns also change dramatically. They become more adult like, with longer sleep cycles. This abrupt change can be disconcerting for everyone – babies must get used to this new way of sleeping – and parents often find that their tried and true methods of helping their baby sleep no longer work.

6-14 months

Mobility – crawling, standing and walking: These are all new, exciting skills and for many babies, but it also disrupts their sleep. You may see your baby rocking back and forth on all fours on their crib. Other babies pull themselves up and call out when they can’t get back down. This increased mobility might also make them more hungry, which could make them wake for a feed.

9-24 months

Talking: A burst of language development causes exciting new things to fire in your baby’s brain. You may hear them practising new sounds and words as they go to sleep or in the night.

6-24 months

Separation anxiety: Babies can show signs of separation anxiety as early as 6 or 7 months, but for most babies it’s at its worst between 10 to 18 months and gets better by two years.

Separation anxiety most often strikes when you leave your child – with a grandparent, or at daycare, for example. But babies can experience separation anxiety at night – for younger babies it’s impossible to understand that you are still there, even if they can’t see you.

With all of these periods, it might be helpful to reframe them as positives – offer you child as much stability as possible, and take comfort in the knowledge that it will pass.

Get to know your baby

While science can’t tell us if there is a ‘right way’ of helping your baby sleep, you can be sure of one thing – tuning into your baby and getting to know his or her individual needs is far more useful than any chart of averages. However, a little understanding about how your child will change at each stage – and what ‘normal’ really looks like – could help you better manage (and ideally reduce!) those sleepless nights.