'Normal' Sleep and 'Sleeping Through'
Where have our ideas about 'normal' infant sleep, and 'sleeping through the night', come from?
Guidelines relating to what is 'normal' for infant sleep, along with popular perceptions of normal or 'problem' infant sleep behaviour, have largely been based upon the research of Moore and Ucko (1957).Moore, T & Ucko, C. 1957. Night waking in early infancy. Archives of Disease in Childhood. 32:333-342. Click here for a summary of this research Based on their study of approximately 160 infants they reported that 70% began sleeping through the night at the age of 3 months. This finding subsequently became codified in paediatric texts and guides for parents as 'infants should be sleeping through the night from 3 months' (e.g. Better Homes & Gardens Baby Book 1965). However this interpretation was misleading on at least 3 counts:
- 'Sleeping through the night' was defined as a 5 hour stretch from midnight to 5am, during which the parents were not woken by the baby's crying or fussing. However prevailing infant care fashions at the time meant that parents were putting their infants to sleep in a separate room, so although parents may not have been woken by their infant, it is likely that infant wake time was underestimated (Anders 1979).
- Although at 3 months 70% of infants began experiencing 'sleeping through', 30% did not do so until later. Additionally, although sleeping through may have been experienced by 3 months, the researchers did not report the babies were regularly sleeping through the night. Reverting back to frequent night waking was common - Moore & Ucko report that half of their sample reverted back to night waking regardless of the age at which parents believed they had begun 'sleeping through'.
Moore & Ucko's study was done at a time when infants were predominantly fed cow's milk based formula, and supplemented early with 'baby rice' or 'infant cereal'; we now know that what an infant is fed affects both their sleep patterns and the frequency of parent-infant interactions during the night.
Recent research by Henderson et al (2010)Henderson et al. 2010. Sleeping Through the Night: The Consolidation of Self-regulated Sleep Across the First Year of Life. Pediatrics. 126(5):e1081-e1087. Click here for a summary of this research investigated infant night-time sleep development from birth to 12 months against 3 criteria:
Criterion 1: sleeping uninterrupted from 24:00 to 05:00 hours (from Moore and Ucko); Criterion 2: the 8-hour criterion, sleeping uninterrupted for 8 hours minimum between sleep onset and time awake in the morning; Criterion 3: the family-congruent criterion, sleeping uninterrupted from 22:00 to 06:00 hours." (p1083) Infants were judged as having met the criterion of having 'slept through' if they had done so for 5 of 6 reported nights in one week, or on 80% of occasions if there were missing data.
Henderson et al found that at 3 months, 58% of infants met criterion 1, at 4 months 58% met criterion 2, and at 5 months 53% met criterion 3; and concluded that criterion 3 should be used by clinicians to define 'sleeping through the night' for infants from 4 months old as it is "met by 50% of infants at 5 months of age, is congruent with family sleep patterns, and falls within typical sleep times" (p1086).
However, by the time they reached 12 months of age, 27% of infants still did not meet criterion 3. Despite this, Henderson et al recommend that "interventions intended to prevent infant sleep difficulties" be implemented in the first 3 months of life. Although Henderson et al have made some contribution to defining a socially relevant meaning of 'sleeping through the night', the relevance of their inferences about the development of normal sleep consolidation - on any of their three criteria - is limited by lack of data on either infant sleep location or infant feeding method, both of which are known to have a profound impact on real and perceived sleep duration. See here for more information on this.