New parents are told that babies wake frequently and are rarely told why, which leaves the impression that something is wrong when nothing is.
Sleep cycles
Adults cycle through sleep stages over roughly ninety minutes.
Newborn cycles are considerably shorter, which means more transitions between stages and more opportunities to wake fully.
Which is a structural difference rather than a habit, and it changes gradually over the first year.
Active sleep
Newborns spend a much larger proportion of sleep in the active state, which is the precursor to what becomes rapid eye movement sleep.
During it they move, make noises, and their eyes move under the lids, which frequently looks like waking.
Which means a baby appearing to stir is frequently in active sleep rather than waking, and intervening can wake them fully.
The proportion of active sleep decreases across the first months.
Circadian development
Newborns have no established day-night rhythm, since the internal clock develops over the first months.
Which is why newborn sleep is distributed across the twenty-four hours rather than concentrated at night.
Light exposure, particularly daylight in the morning, is the main signal that entrains the developing rhythm.
Melatonin production begins developing at a few months of age rather than being present from birth.
Feeding
Small stomach capacity and rapid digestion mean frequent feeding is a physiological requirement rather than a preference.
Which is the reason for much night waking in the early months, and it decreases as capacity increases.
What the guidance actually says
Safer sleep advice from health authorities is specific and consistent across countries on the main points.
Babies sleeping on their back for every sleep.
A clear flat sleep surface with no loose bedding, pillows or soft objects.
Sleeping in the same room as the parent for the first months.
Avoiding overheating.
And a smoke-free environment.
These recommendations are based on substantial epidemiological evidence and are worth following precisely rather than approximately.
Sleep training
A contested area where the evidence is more limited than the confidence on either side.
Trials of behavioural approaches in infants over six months have generally found improvements in parent-reported sleep and parental mood.
Follow-up studies have not found the harms that critics predicted, and the studies have limitations that critics identify.
Which means the honest position is that some approaches work for some families over some age ranges, and that the evidence does not support strong claims in either direction.
It is not appropriate for young infants, and any approach should be discussed with a health professional if there is any concern.
Realistic expectations
Population data on infant sleep shows enormous variation, with night waking common well into the second year.
Which means comparison with other babies produces anxiety without information, since the range of normal is very wide.
When to seek advice
Difficulty breathing, unusual pauses in breathing, poor feeding, unusual lethargy or any concern about a baby's wellbeing warrant contacting a health professional promptly.
Parental exhaustion is itself a reason to seek support, since it is common, has real consequences and is treatable.
Room sharing and bed sharing
Distinct arrangements with different guidance.
Room sharing without bed sharing is recommended by health authorities for the first months, with evidence associating it with reduced risk.
Bed sharing carries increased risk in specific circumstances, which health services set out explicitly — smoking, alcohol or drug use, extreme tiredness, sofas or armchairs, low birth weight and prematurity.
Which is why guidance now generally addresses how to make it safer rather than only advising against it, on the reasoning that many parents do it and unplanned bed sharing on a sofa is more dangerous than a planned safer arrangement.
The specific guidance for your country is worth reading, since the recommendations are precise.
Swaddling
Practised widely and requires care.
Hips must be able to move freely, since tight wrapping of the legs is associated with hip development problems.
It must stop once a baby shows any sign of rolling, since a swaddled baby who rolls cannot right themselves.
And overheating is a specific concern.
Parental sleep
Sleep deprivation in new parents is severe and affects judgement, mood and safety.
Which means arranging for one parent to get a protected block of sleep, sharing nights, and accepting help are practical rather than indulgent.
Driving while severely sleep deprived carries risk comparable to alcohol impairment in several studies.
Naps
Daytime sleep consolidates gradually, from many short periods toward a smaller number of longer ones.
Which follows a fairly consistent developmental sequence, with the number of naps reducing across the first years.
Overtiredness makes settling harder rather than easier, which is counter-intuitive and well documented.
Regressions
Periods where established sleep deteriorates, frequently coinciding with developmental milestones.
Which are described widely and are less precisely defined in research than the popular accounts imply.
The general pattern of sleep disruption around developmental change is real, and the specific ages given are approximate.