You’re running on two hours of sleep. The baby is wide awake at 3am. And you’re Googling “when do newborns sleep through the night” for the fourth time this week. And then they have the audacity to nap trap you all morning when there’s washing, hoovering, and breakfast to think about.
Before you became a parent, you were probably told to expect tiredness. But what you might not have expected is just how unpredictable and unhinged your newborn sleep schedule really is.
Frustrating though it might be, there’s a logical reason why young babies’ sleep is all topsey turvey is, and knowing it – as well as when things might start to improve – certainly helped make those bleary-eyed nights (and days!) feel a little more bearable for us.
Why we sleep
To understand why newborn sleep is so chaotic, it helps to first understand how adult sleep is regulated. In grown-up bodies, two powerful systems work together to keep us sleeping at night and awake during the day. (If you want to go deep on exactly how these differ from your baby’s sleep, we’ve got a whole podcast on how baby sleep and adult sleep compare.)
Sleep-wake homeostasis is the first.
This is the biological pressure to sleep that builds with every hour you spend awake. The longer you’ve been up, the stronger the urge to sleep becomes, until eventually you simply can’t fight it. And once you do sleep, the length of your sleep roughly matches how long you were awake.
Circadian rhythm is the second.
This is your internal body clock, a roughly 24-hour cycle synced to the day-night pattern of the world around you and regulated by hormones in the body. When darkness falls, your brain releases melatonin, the hormone that signals it’s time to sleep. Come morning, cortisol takes over, sharpening alertness and preparing you for the day. Your core body temperature also follows this cycle, dipping at night to help you stay asleep and rising back to normal during the daytime.
These two systems working in concert are what give adults reliable, consolidated sleep. The problem? Newborns have neither.
Why Newborns Sleep Differently
Their circadian rhythm hasn’t switched on yet
Newborns don’t produce melatonin in meaningful amounts until they’re about two to three months old. Without it, there’s no hormonal signal telling them that darkness means sleep. To all intents and purposes, day and night are identical to a brand new baby.
Their body temperature doesn’t follow a day-night cycle either. It stays relatively constant regardless of the time, removing another of the physical cues that anchor adult sleep to nighttime.
Research suggests that the physiological functions regulating sleep, including melatonin secretion and body temperature rhythm, don’t begin to emerge until at least eight to eleven weeks of age in healthy, full-term babies.
Their sleep drive is easily overridden
Young babies do experience some version of homeostatic sleep pressure, that building urge to rest, but it’s easily overridden by more urgent needs. Chief among them: hunger.
A newborn’s stomach is roughly the size of a marble. It empties fast, and when it does, the hunger signal is powerful enough to override any sleepiness. This is why newborns typically wake every two to three hours to feed, around the clock, regardless of whether it’s 2pm or 2am.
You may have heard that formula-fed babies sleep longer stretches because formula digests more slowly. There’s something to this, though the picture is more complicated than it first appears.
Both systems are simply immature
Both the homeostatic and circadian processes are underdeveloped in babies, and this accounts for the dramatic differences in sleep between infants and adults. It’s not a flaw. It’s a developmental stage.
How Can You Help Your Baby’s Sleep Develop?
When you’re sleep deprived, you’ll try almost anything. And the internet is full of tips, including some long-held folk theories like flipping your baby upside down (don’t do this!). Some of this info has got science backing, but the picture is typically more complicated than you might imagine. While you can’t rush biological maturation, there are things that may support it.
Light exposure matters.
Exposing your baby to natural light during the day and keeping things dark and calm at night can help the developing circadian system begin to calibrate. The brain uses light as its primary cue to set the body clock. Even in newborns who aren’t yet producing melatonin, regular light and dark exposure may help get those systems going sooner.
A calming bedtime routine can help.
Babies are highly sensory creatures. Warmth, rhythm, closeness, and familiar sounds all signal safety and can ease the transition to sleep. This is partly why rocking, white noise, and skin-to-skin contact tend to work so well in the early weeks. Scientists have also helped to develop a lullaby to emulate a calming, womb-like environment. If your baby seems to need a lot of sensory input to settle, you’re not alone. Sensory seeking at bedtime is very common at all infant ages.
Feeding patterns will naturally space out.
As your baby grows, their stomach capacity increases and they can go longer between feeds, which means longer stretches of sleep. This happens on its own, though feeding on demand in the early weeks is important for supply and for your baby’s growth.
Diurnal rhythms emerge gradually.
Studies show that consolidated rhythms, including the cortisol cycle that anchors daytime alertness, begin emerging between around six and eighteen weeks. Night sleep starts to consolidate alongside this shift.
A note on sleep environment. Some parents find that keeping baby close at night, whether through a bedside crib or co-sleeping, makes those frequent waking easier to manage. If you’re considering co-sleeping that might really help co-regulate, it’s worth reading about the Safe Sleep 7 guidelines to understand how to do it as safely as possible.
When Does It Get Better
The reassuring truth is that things do improve, and they improve naturally. Most babies begin producing melatonin around two to three months. Their stomachs grow. Sleep gradually consolidates into longer blocks and, with any luck, more of those blocks will fall at night.
Most parents notice a meaningful shift somewhere between three and six months, though every baby is different and “sleeping through the night” remains a moving target for many families well beyond that. Not to mention the famous four month regression! Hard though it may be for parents, those night-times wakes are perfectly normal and actually protective for your little one.
For now, if you’re in the thick of the newborn stage: you’re not doing anything wrong. Your baby’s sleep is all over the place because their brain and body aren’t yet equipped to do otherwise. It will get better, I promise.
The Science Baby 
Leave a comment