It is important to remember that sleep is a developmental process, and that sleep needs will change throughout our lifetimes.
Newborn babies may sleep for 18 or so hours a day, but often for only for 2-3 hours at a time. During the first year overall sleep duration falls to around 15 hours, and the majority of sleep becomes concentrated during night-time as the circadian rhythms develop .
A recent systematic review drew together data from 34 studies relating to normal infant sleep duration. The chart below shows part of this data for babies aged up to one year. Data from each study & age range are represented by a dot which shows the average total sleep experienced. The dotted line shows the amount of variation around that average. It is clear that younger babies sleep longer overall, but there is also a lot of variation among individual babies, and within studies, for this group.
Night-waking is normal during early infancy and healthy babies experience several awakenings per night at the end of sleep cycles.
Newborn babies have very small stomachs, and need to feed often, so they wake at least every 2-3 hours in order to do so, sometimes more often. As babies grow, they are able to last slightly longer between feeds, however, human milk is quickly digested, and babies commonly need to feed frequently throughout the day and night-time.
By the time babies are 3 months old some (but not all) begin to start settling (sleeping through a night-time feed for a stretch of up to 5 hours). By the time they are 5 months old half of them may have started to sleep for an eight-hour stretch on some nights. Generally, though, babies do not sleep all night-every night until they are close to a year old. One study investigating infant sleep duration found that 27% of babies had not regularly slept from 10pm to 6am by the age of 1 year. 13% of babies had not regularly slept through for 5 hours or more by the age of 1 year.
Popular beliefs about when babies should be 'sleeping through the night' are based on studies conducted in the 1950s and 1960s on groups of formula-fed babies. However, it is normal for babies - especially breastfed babies - to wake and feed at night throughout at least the first year.
Encouraging babies to 'sleep through' before they are ready to do so makes it difficult to keep on breastfeeding, and may encourage babies to develop mature sleep patterns out of sequence with their other circadian patterns such as those controlling the regulation of temperature, hormone production, and the genes that control our biological rhythms.
More detailed information about normal sleep for babies can be found on our Health Practitioners pages.