Newborn sleep (0-3 months): rhythm and safe sleep

Day/night reversal: an almost universal stage

A newborn doesn't yet have an internal clock to tell day from night. In the womb there was no light or darkness to follow, only the mother's rhythm. They can therefore sleep for long stretches in the middle of the day and be wide awake in the middle of the night, with nothing abnormal about their behavior. According to the UK's National Health Service (NHS), a newborn's total daily sleep varies but can be around 18 hours, and babies wake at night because they need to be fed.

A study that followed 35 full-term infants from the sixth to the eighteenth week measured the appearance of these biological rhythms week by week. The rhythm of cortisol, a hormone, showed up first, at about 8 weeks. The melatonin rhythm followed roughly a week later, just as night sleep was starting to consolidate (Joseph et al., Archives of Disease in Childhood, Fetal and Neonatal Edition, 2015).

Nothing parents do or don't do really speeds this stage up before the age at which it happens naturally. Night feeds, frequent at this age, answer a real need, digestive as much as relational, without creating a bad habit to fix later.

How should a newborn sleep safely?

To sleep safely, a newborn is placed on their back, on a firm, flat surface, with no soft objects. The American Academy of Pediatrics recommends this position for every nap and every night until the first birthday. A newborn's sleep setup is one of the few areas of child sleep where recommendations rest on a solid international consensus, updated regularly as research advances.

The sleep surface matters as much as the position: a firm, flat mattress that doesn't sink under the baby's weight, covered with a well-fitted sheet and nothing else. Pillows, comforters, crib bumpers, stuffed toys, and positioning cushions have no place in an infant's bed, however cozy they look. Those soft objects are exactly what raises the risk of suffocation.

Sharing the parents' room, without sharing their bed, on a separate sleep surface, is also part of the American Academy of Pediatrics' recommendations for at least the first six months. The NHS gives the same advice: a separate cot or Moses basket in the parents' room for every sleep, for at least six months. The baby stays within sight and earshot, without sleeping on the same surface as an adult. The NHS also advises against bed-sharing if either parent smokes, has had alcohol, has taken drugs or a medicine that causes drowsiness, or if the baby was born before 37 weeks or weighed under 2.5 kg at birth.

In France, the Haute Autorité de santé (HAS, the national health authority) gives the same guidance: always place the baby on their back, in their own bed, ideally in the parents' room for the first six months and without sharing the parents' bed. It also asks for a firm mattress with no pillow, duvet or blanket, a room kept at 18 to 20 °C, and no exposure to tobacco. Head-positioning cushions, cot bumpers and similar devices are discouraged. The French health insurance service (ameli.fr) and the official 1000 premiers jours site repeat these points and recommend a correctly sized sleeping bag instead of blankets.

These recommendations apply wherever the baby sleeps. Inclined seats and devices (car seat, stroller, bouncer, baby carrier) aren't suited to routine sleep, especially before 4 months: a baby who falls asleep in one is better off moved to a firm, flat surface as soon as possible. A couch or armchair, with an adult who might doze off, is to be avoided in all circumstances. These recommendations never replace individual medical advice: a pediatrician remains the right person to ask about any question specific to a given baby.

Soothing gestures, before the rhythm sets in on its own

Before the circadian rhythm sets in on its own, it's better to mark the contrast between day and night than to impose a fixed bedtime or an elaborate ritual. A newborn doesn't yet have the biological landmarks to hold onto, while a clear contrast in the environment helps more, even if the baby doesn't adapt right away.

During the day, let in natural light and keep up the household's usual activity and noise while the baby naps. At night, do the opposite: keep lights low and exchanges brief and calm during feeds or diaper changes, even when the baby is wide awake.

What soothes varies a lot from baby to baby: rocking, carrying, steady background noise. It's adjusted by trial and error rather than from a universal manual. At this age, the priority is still safe sleep, not a polished routine.

What a typical day looks like at six weeks

At six weeks, a typical day mixes naps spread with no fixed schedule and nights still chopped up by feeds, and that's normal. In the morning, for example, you open the curtains and keep the baby in the main room, among the ordinary noises of the house. In the afternoon, they nap on their back in their bassinet, and the house doesn't have to go quiet.

In the evening, the light drops and so do voices. At 2am, a bedside lamp is enough for the feed, you talk little and quietly, and you put the baby back down on their back as soon as they're full, without playing. They wake again at 5. At six weeks, that script is ordinary, not a failed night.

At what age do babies tell day from night?

The day/night rhythm sets in gradually, most often around 2 to 3 months, and almost never all at once. As biological rhythms fall into place over the weeks, nights stretch into longer and longer blocks, and daytime naps gradually cluster at more predictable times.

Around 2 to 3 months, most babies already sleep longer stretches at night, even if waking to feed stays frequent and normal at this age. The NHS notes that between 3 and 6 months, night feeds drop off and some babies sleep 5 to 8 hours in a row, but not all. It's also when sleep benchmarks by age become relevant, when they hardly made sense before: the American Academy of Sleep Medicine gives no range before 4 months.

If your 3-month-old isn't doing long nights yet, that isn't a delay. If you're unsure about their sleep, their breathing during sleep, or their weight gain, the pediatrician is the right person to ask, well before any online guide.