Sleep
Sleep regressions, and whether they are real
The ages are not fixed and the underlying phenomenon is genuine: development disrupts sleep, repeatedly.
Sleep regression is not a clinical term, and the phenomenon it describes is real enough that dismissing it entirely does parents a disservice.
The four-month change
The one with a genuine physiological basis, and the reason it is not really a regression.
Newborn sleep has two broad states.
Around three to four months, sleep architecture matures towards the adult pattern with distinct stages and more defined cycles.
Which means more transitions between cycles and more opportunities for a baby to surface and notice their circumstances have changed since they fell asleep.
This is a permanent developmental change rather than a phase that reverses, which is why sleep after four months frequently does not return to what it was.
What helps: putting the baby down drowsy but awake at least sometimes, a consistent bedtime routine, a dark room, and adjusting expectations.
The other commonly cited ages
Where the evidence is weaker and the observation still holds.
Around eight to ten months, coinciding with crawling, pulling to stand, separation anxiety and frequently teeth.
Around twelve months, coinciding with walking and a nap transition.
Around eighteen months, coinciding with language development, autonomy and molars.
Around two years, coinciding with imagination, fears and cot-to-bed transitions.
The specific ages are approximate and vary between children — what is consistent is that periods of rapid developmental change disrupt sleep.
Why development disrupts sleep
Plausible mechanisms.
New motor skills are practised involuntarily, including at three in the morning — a baby learning to stand will stand in the cot and then be unable to sit down.
Cognitive changes alter what the baby understands, and object permanence means realising a parent still exists elsewhere, which is why separation anxiety and night waking coincide.
Increased daytime stimulation and learning affects sleep consolidation.
And nap transitions create temporary mismatches between sleep need and sleep opportunity.
What to do
Mostly to hold the line rather than to introduce new solutions.
Keep the routine consistent, since predictability helps most during disruption.
Give plenty of daytime practice of the new skill, which reduces the night-time rehearsal.
Increase daytime connection during separation anxiety phases.
Offer more comfort temporarily, which does not create permanent habits in a few weeks.
Watch for the nap transition and adjust rather than fighting it.
And use an earlier bedtime during disrupted periods, since overtiredness compounds everything.
What not to do
Introduce a completely new approach in the middle of a disrupted period, which rarely works and generally makes it worse.
Assume it will last, since these periods typically last one to a few weeks.
Drop a nap because of a few bad days, since regressions frequently cause temporary nap refusal that resolves.
And blame yourself for something you have done, since the timing is developmental and not behavioural.
When it is not a regression
The important exclusions.
Illness, including ear infection, which classically causes waking and distress when lying flat.
Teething, which affects sleep for a few days around an emerging tooth rather than for months — attributing months of poor sleep to teething is one of the most common misattributions and delays finding the actual cause.
Reflux, allergy or eczema causing discomfort.
Obstructive sleep apnoea, where snoring, mouth breathing and restless sleep are the signs.
Iron deficiency.
Changes in circumstance: a new carer, starting childcare, moving house, travel or a new sibling.
And an environment that has changed — a lighter room in summer, a warmer one, a noisier one.
Surviving it
Practical rather than optimistic.
Share the nights explicitly, so that one person gets a block of sleep rather than both getting fragments.
Lower every other standard for the duration.
Go to bed earlier yourself, which is the only variable you control.
Get outside in daylight, which helps both of you.
And keep a rough record, because in three weeks you will not remember whether this started before or after the new tooth, and the pattern is what tells you what it was.
General information only, not medical advice. Consult a health visitor or clinician if sleep disruption is prolonged, or if your child snores or seems unwell.
