This is the final sleep research post. I hope people have found them useful!
If you find this post interesting, you may also be interested in What is a Normal Sleep?, Effectiveness of Controlled Crying, Risks of Crying Methods, and Viewing Crying Methods in Perspective.
Because crying methods are controversial, and because they were a staple of Western parenting methods for much of the 20th century, there is quite a lot of research about them. Comparatively, the research on non-crying methods is sparse. The way I have approached this post is to summarise the research I have found by technique.
Be calm, affectionate, and responsive when you put your child to bed
There have been a lot of studies about what parents do when they put children to sleep (eg. pat, nurse, leave to cry etc.), but little research about how they do it. A 2010 study (Teti) looked at the question: does it matter how emotionally available the mother is when she puts the baby to bed? The study looked at 39 families with infants between 5 weeks and 24 months old.
What it found is that the more mothers assisted their infants to wind down with sensitive, calm, affectionate, and responsive behaviour (including gazing into the child's eyes while nursing, cuddling, quiet play such as reading a book or gentle talking, not persisting in forcing the child into an activity they did not want to do, not showing irritation or anger towards the child, and not leaving the child to cry or at least not leaving the child to cry for no longer than a minute), the easier the child settled to sleep and the less sleep disruptions they caused during the night. The combination of sensitive, calm, structured, and affectionate behaviour was described as maternal 'emotional availability'. (An example of a mother who scored low on 'emotional availability' was one who persisted in trying to read to her child when he wasn't interested, pulled him back into bed when he got out, and threatened to take away his toys unless he went to sleep.)
Whether the mothers particularly cuddled, nursed, patted, or read to their babies did not show any relationship to sleep quality. It was how they did these things that mattered. The study controlled for the mothers' age, education, family income, employment status, co-sleeping or separate sleeping arrangements, and found none of these factors were relevant to sleep quality in the families studies (although the sample was probably fairly homogenous).
The authors suggest that the reason why emotional availability helps children sleep is that feeling safe in one's sleep environment assists sleep.
One treatment for night-wakings is 'scheduled waking'. This is where parents are instructed to wake their child 15-60 minutes before the child usually wakes and to resettle the child to sleep. In one study of 33 children between 6 and 54 months, this has been found to significantly reduce the number of night wakings as much as crying it out, although the method took longer to take effect (Rickert and Johnson). This has been observed to be reasonably effective by a number of studies but it can be hard for parents to stick to (Mindell).
In one study of 36 children aged between 18 and 48, all with settling problems, implementing a positive bedtime 'wind-down' routine was compared with crying it out. The study found that the wind-down routine was as effective as controlled crying in reducing settling problems (Adams and Rickert).
Co-Sleeping & Room Sharing
Co-sleeping works differently from other sleep training methods. Instead of training the baby to do anything, it adjust the environment so night wakings become more palatable to mum.
A 1994 study of 50 9-24 month old infants with sleeping difficulties compared co-sleeping and controlled crying. Half the infants were treated with controlled crying. The other half required only that a parent sleep in the same room as the child. Sleeping in the same room as the child was as effective as controlled crying. Both reduced parental perceptions of a sleep problem by 60%, and actigraphy recordings showed that both resulted in significantly more sleep for 52% of the children (Sadeh).
Does co-sleeping affect night wakings or daytime behaviour?
Studies have shown that co-sleeping babies sleep more lightly and have more frequent night-wakings, but also that mothers and babies who are co-sleeping have sleep cycles that fall into sync (Mosko, Richard, and McKenna). What this means is that yes, co-sleeping babies tend to wake more, but that the wakings can be less disruptive for the mother because she is not woken unexpectedly out of deep sleep but comes into semi-waking naturally and is able to address the infant's needs quickly and return to sleep easily.
One study looked at differences in behaviour between 83 pre-school children who: a) co-slept at infancy, b) solitary sleepers in infancy but started to co-sleep at or after age one; or c) didn't co-sleep. The study found that solitary sleepers fell asleep alone and slept through the night a full year to year and a half earlier than co-sleepers, and at pre-school age co-sleepers woke 'sometimes' whereas solitary sleepers woke 'rarely'. Another study of 6 month old Swedish infants found that co-sleeping was associated with waking more than 3 times a night, although it was not clear at this age whether co-sleeping caused the waking, or the waking caused parents to try co-sleeping (Möllborg et al).
However, children who had co-slept since infancy 'were more self-reliant (e.g. ability to dress oneself) and exhibited more social independence (eg. make friends by oneself)' during the day. They also breastfed for longer. There was no difference between the groups on when the children were toilet trained (Keller and Goldberg).
The study found that early co-sleeping tended to be part of a deliberate style of parenting that encourage the child's autonomy through being 'baby-led' – however even when controlling for this parenting style, early co-sleeping had a positive effect on infant independence. More of the deliberate co-sleepers had children night wakings than the parents with solitary sleepers, but the early co-sleepers psychologically adjusted to having the baby in the bed and found the night wakings more rewarding than disruptive (Keller and Goldberg). By contrast, babies who were solitary sleepers in infancy and who later became co-sleepers had frequent, disruptive night wakings (Keller and Goldberg). This is consistent with findings that co-sleeping is not associated with sleep problems in cultures where co-sleeping is routine, such as China (Jiang et al), and Japan (Latz et al). In Egypt where co-sleeping is normal, teenage co-sleepers were found to have better sleep and solitary sleepers to have increased sleep dysregulation (Worthman and Brown).
It is also consistent with another study that found parents who co-slept every night and parents who slept apart from their babies every night at 6 months had more positive interactions with their babies at 9 months, whereas parents who some nights slept with their babies and some nights did not had much less positive baby-parent interactions (Taylor et al). In addition, mothers who co-slept at 6 months were found to have less maternal depression at 9 months than both the solitary sleepers and the inconsistent co-sleepers (Taylor et al).
If you co-sleep with your baby, how long can you expect to co-sleep for?
It appears that if you stop before 9 months, it is no more likely that you will co-sleep with your child as they get older than if you had never co-slept at all. However, after this time, a persistent pattern of co-sleeping is likely. In a longitudinal study, 493 Swiss babies were followed from birth until 10 years of age to track bed sharing and night waking. This study found that less than 10% of children shared a bed with their parents in the first year of life (bed-sharing defined as sharing the bed at least once a week), but by 4 years, 38.1% of the children were sharing a bed at least once a week. At 8 years, 21.2% of the children were sleeping at least once a week in their parents bed and 5.1% did so every night. Interestingly, the study found that children sharing a bed with parents at 6 months old were not more likely to share the parents' bed during childhood than children not sharing at that age. However, children who were bed-sharing at 9 and 12 months tended to persist in bedsharing for 3 years.
In a study of deliberate early co-sleepers, many expressed the view that the child initiated a move to his or her own bed before th e age of three, and that it was a smooth, happy transition (McKenna and Volpe).
Is co-sleeping safe?
Bed sharing is associated with a higher risk of SIDS, but it is important to recognise that it is not sharing a bed that is the cause of this higher risk. It is infants being placed on their side (who then role onto their tummies), bedding in the bed which may smother the infant or make them too hot, sleeping with your baby on a sofa, sleeping with your baby and another child, or bed-sharing while intoxicated or if mum smokes (Ostfeld, Middlemiss, Blair). The exact reason why smoking is a risk is not known – it may be due to effects of smoking chemicals passing into the baby's body in utero, or it may be that residual chemicals in the mother's mouth and lungs are breathed out onto the baby while they are sleeping, affecting the air quality and elevating the risk of SIDS.
However, bed sharing has also been associated with a longer duration of breastfeeding (Möllborg et al), and breastfed babies have a significantly reduced likelihood of SIDS. Therefore, if you are sleep deprived and considering making a choice between changing to formula feeding (so you can share the burden of night feedings with your partner, and so the baby sleeps longer between feeds, which is regularly the case with formula) or co-sleeping – don't assume that cot-sleeping with formula is the safer choice. Breastfeeding appears to be far more protective than safe co-sleeping is dangerous. Statistics gathered on co-sleeping are so muddled by the inclusion of unsafe co-sleeping arrangements (unsafe bedding, intoxicated mothers who roll onto their infants etc.) and the variable of breastfeeding (as co-sleeping is highly correlated with breastfeeding, which is highly protective of SIDS, breast-fed babies are about half as likely to die of SIDS – see Venneman) that it is currently impossible to say.
As James McKenna argues, because the Western world has come to accept solitary sleeping as the cultural norm, this shapes the way statistics are gathered. So when an infant dies in a cot, solitary sleeping is never presumed to be the cause, and if no cause is apparent, the death is written off as the mysterious 'SIDS'. By contrast, if an infant dies when co-sleeping, it is frequently presumed that overlying must have occurred, even if there is no evidence of this (McKenna and McDade). It is also assumed that co-sleeping occurs very rarely, which makes it look like co-sleeping deaths occur frequently among a small number of co-sleepers. In practice, very large numbers of women co-sleep occasionally, and up to about a third co-sleep regularly (Hauck et al., 2008), but the amount of co-sleeping is underreported, not least because many women do not like to admit they engage in a purportedly 'dangerous' practice.
Co-sleeping babies sleep lighter than babies who sleep alone. It has been proposed that co-sleeping may protect against SIDS by helping babies to regulate their sleeping patterns and avoid stopping breathing (Mosko, Richard, and McKenna). While this is a logical theory, and perhaps explains why infants sharing a room have a lower rate of SIDS, there is no evidence yet as to whether it actually works in practice. A counter-argument is found by one study of 5 week and 6 month old babies has found that when usually co-sleeping babies are put to sleep on their own, they actually sleep more heavily with less active and more quiet sleep (Hunsley and Thoman). They argue that this puts co-sleeping babies at greater risk for SIDS when they are not sleeping with an adult (eg. day sleeps). As of 2000, the American Academy of Pediatricians Task Force on Infant Sleep Position and Sudden Infant Death Syndrome neither advocated or warned against co-sleeping, however, they noted that the following were hazardous ways of co-sleeping (Task Force):
• If a mother chooses to have her infant sleep in her bed to breastfeed, care should be taken to
observe the aforementioned recommendations(nonprone sleep position, avoidance of soft surfaces or loose covers, and avoidance of en-trapment by moving the bed away from the wall and other furniture and avoiding beds that present entrapment possibilities).
• Adults (other than the parents), children, or other siblings should avoid bed sharing with an infant.*
• Parents who choose to bed share with their infant* should not smoke or use substances, such as alcohol or drugs, that may impair arousal.
It is interesting to note that overlying the baby is not the biggest risk of co-sleeping, it is (similarly to a poorly made cot) entrapment between the bed and the wall (about 50% of co-sleeping deaths), or entrapment between the mattress and another part of the bed such as a bed-rail (about 30% of co-sleeping deaths) (Scheers et al). The very worst place to co-sleep with your baby is the sofa (Task Force). In the Chicago Infant Mortality Study, the deaths of 260 infants were explored and it was found:
“An increased risk of SIDS was observed for bed sharing, but multivariate analysis indicated that the risk was primarily associated with bed sharing when the infant was sleeping with people other than the parents.” (Hauck et al)
A side note on the Hunsley and Thoman study: Because less active and more quiet sleep can be a response to severe stress, such as circumcision, the authors of this study decide that the co-sleeping babies were severely stressed when sleeping alone (as opposed to non co-sleeping babies who sleep alone). This may or may not be true since the stress levels of the babies weren't measured. The idea that less active and more quiet sleep indicates severe stress has been derived from studies that did not specifically look at stress patterns in babies who co-sleeping. As co-sleeping affects the way infants sleep, the heavier sleep when apart from parents may simply be normal for co-sleepers, and not an indication of stress. The other problem with the conclusion is the presumed direction of the causality. Even assuming the babies are stressed, an alternative and equally plausible hypothesis is that a generally high level of stress (from the infant's biology or environment) when being put to bed caused both infant fussiness, and the co-sleeping more than twice a week. It is therefore the stress that causes the co-sleeping, not the co-sleeping that causes the stress. 'Usually co-sleeping' in this study was defined as infants who co-slept twice a week or more for at least 6 months. This is a problematic definition of co-sleeping, because it includes infants who are co-slept with reactively in response to temperamental sleep problems as well as infants who are co-slept with for philosophical reasons. It is likely the study included primarily reactive co-sleepers given that infants were selected for the study if they exhibited 'fussiness' that was troublesome to the parents. It may well also have captured parents who employed methods such as letting the child cry to sleep when the child slept alone, a method that might be all the more stressful for a child if it was applied inconsistently – and combined with sporadic co-sleeping.
Fable & Reward
A small 2004 study of 4 children (aged 2, 5, 7 and 7) with severe tantrums at bedtime, 'treatment' was to add a story at the end of the child's usual bedtime routine. The story was called The Sleep Fairy and it was the story of two children who learned to go to bed without fuss and were, as a result, rewarded by the sleep fairy. If the child settled well and stayed in bed, parents were to place a simple reward (eg. a sticker) under their pillow for the children to find in the morning. Sleep problems rapidly reduced and were maintained at a 3 month follow up for all children (Burke).
A study on 19 children between 3 and 6 years combined crying it out with a 'bedtime pass'. Upon going to bed each child was given a card which was a 'free pass' to leave the room and come out for parental attention. If they cried out beyond this they were ignored. The study found that children given the pass cried out significantly less than children who were just ignored, and that all children given the pass had stopped using it at the 3 month follow-up (Moore et al). Families using the 'bedtime pass' were compared to families who ignored the children without a pass, and improvements in the number of times the children left the bedroom were similar in both groups.
Put Your Child To Bed Later
This revolutionary idea is – if your baby fights sleep, perhaps she or he is not tired. A study compared babies born in the late 70s, early 80s, and late 80s-early 90s. It found that parents in the late 70s tried to put their babies to bed earlier and had far more bedtime resistance (Jenni et al 2005). As discussed in 'what is a normal sleep' below, individual babies need different amounts of sleep.
Be Happy With What You Do
There is increasing evidence that in the majority of cases, it is not the amount of night wakings that parents find stressful, it is their confidence in responding to those wakings. Deliberate co-sleepers tend to be happy with their choice, as do deliberate sleep-trainers. But those who try sleep training but whose babies don't respond, and those who take up co-sleeping because keeping on re-settling the baby elsewhere is too exhausting are those who report the greatest 'sleep problems' (Goldberg and Keller). This does not mean you have to pick on strategy and stick to it. Indeed, a large British study has found that your best bet at avoiding sleep problems is to be responsive to your child's needs and adopt a variety of strategies, including actively assisting your child to settle when they need it (Morrell and Cortina-Borja).
Mothers who are inconsistent co-sleepers (again, most likely reactive co-sleepers) tend to have poorer quality interactions with their bubs than those who are consistent with co-sleeping or non-co-sleeping (Taylor et al). Inconsistent co-sleeping was defined as sleeping 1-6 nights a week in a parental bed, whereas consistent co-sleeping was sleeping even night in a parental bed, though not necessarily for the whole night. The mums with consistent sleeping arrangements were more positive in interacting with their babies and had greater sensitivity in responding to their babies, and the babies were more interactive and cheerful. The study controlled for duration of breastfeeding, infant temperamental intensity, hours worked by the mother, and maternal depression. It did not, however, control for the reason why the inconsistent co-sleeping was employed, or whether the effect on interaction was not due to the sleeping style per se but that sleeping style was indicative of whether mothers had consistent or inconsistent parenting styles generally.
A study of 52 infants at 10 months looked at whether the mother's general level of separation anxiety affected the sleep of the infant, and found that higher levels of maternal anxiety was correlated with more night-waking episodes – statistically, it seemed to affect 9% of night wakings. This was true of actigraphy recordings, not just the night wakings mothers were aware of. Mothers who had high levels of separation anxiety were more likely to assist their child to sleep with active settling, but the maternal anxiety had an effect on night wakings over and above the effect of active settling. This suggests there are some children who settle well with active settling, provided the mothers do it in a calm and structured way and respond to daytime separations in a calm and structured way, and that there are some children who can't learn to self-settle because the mothers are too anxious (Scher 2008).
Medical reasons for sleep disturbance
Approximately 17% of children have anxiety disorders, and approximately 88% of children with anxiety disorders have a sleep-related problem, such as insomnia and reluctance to sleep alone. (Chorney et al). Symptoms of sleep disturbance in early childhood has been associated with anxiety disorders when the children grow up to be adults, and fearful children take nearly an hour longer to fall asleep than non-fearful children (Chorney).
Conditions such as asthma and allergic rhinitis have been found to result in poorer sleep (Smaldone). On a personal note, I was a baby who woke at least 5 times a night in distress most nights until I was almost 3 years old, when they finally diagnosed that I had overlarge adenoids and had them surgically removed. My sleep improved instantly. I had been waking up because it was a struggle for me to breathe when horizontal.
Adams and Rickert, 'Reducing bedtime tantrums: comparison between positive routines and graduated extinction' (1989) Pediatrics Vol 84, p756.
Blair et al, 'Babies sleeping with parents: case-control study of factors influencing the risk of the sudden infant death syndrome' (1999) British Medical Journal Vol 319, p1457.
Burke et al, 'Brief Report: A “Storybook” Ending to Children's Bedtime Problems—The Use of a Rewarding Social Story to Reduce Bedtime Resistance and Frequent Night Waking' (2004) Journal of Pediatric Psychology Vol 29(5), p389.
Chorney et al, 'The Interplay of Sleep Disturbance, Anxiety, and Depression in Children' (2008) Journal of Pediatric Psychology Vol 33(4), p339.
Goldberg and Keller, 'Co-Sleeping During Infancy and Early Childhood: Key Findings and Future Direction' (2007) Infant Child Development Vol 16, p457.
Hauck et al, 'Sleep Environment and the Risk of Sudden Infant Death Syndrome in an Urban Population: The Chicago Infant Mortality Study' (2003) Pediatrics Vol 111, p1207.
Hauck et al, 'Infant Sleeping Arrangements and Practices During the First Year of Life' (2008) Paediatrics Vol 122, Supplement 2, pS113.
Hunsley and Thoman, 'The Sleep of Co-Sleeping Infants When They Are Not Co-Sleeping: Evidence That Co-Sleeping is Stressful' (2001) Developmental Psychobiology Vol 40, p14.
Jenni et al, 'Sleep Duration From Ages 1 to 10 Years: Variability and Stability in Comparison With Growth' (2007) Pediatrics Vol 120, pe769.
Jiang et al, ''Epidemiology study of sleep characteristics in Chinese children 1-23 months of age' (2007) Pediatrics International Vol 49, p811.
Keller and Goldberg, 'Co-Sleeping: Help or Hindrance for Young Children's Independence?' (2004) Infant Child Development Vol 13, p369.
Latz et al, 'Cosleeping in Context: Sleep practices and problems in young children in Japan and the United States' (1999) Archives of Pediatric Adolescent Medicine Vol 153, p339.
McKenna and McDade, 'Why babies should never sleep alone: A review of the co-sleeping controversy in relation to SIDS, bedsharing and breast feeding' (2005) Paediatric Respiratory Reviews Vol 6, p134.
McKenna and Volpe, 'Sleeping with baby: An internet-based sampling of parental experiences, choices, perceptions, and interpretations in a western industrialized context' (2007) Infant and Child Development: Special Issue on Co-Sleeping Vol 16, p359.
Middlemiss, 'Infant sleep: a review of normative and problematic sleep and interventions' (2004) Early Child Development and Care Vol 174, p99.
Mindell, 'Empirically Supported Treatments in Pediatric Psychology: Bedtime Refusal and Night Wakings in Young Children' (1999) Journal of Pediatric Psychology Vol 24 (6), p465.
Möllborg et al, 'Bed-sharing among six-month-old infants in western Sweden' (2010) Acta Paediatrica
Moore et al, 'Brief Report: Evaluating the Bedtime Pass Program for Child Resistance to Bedtime—A Randomized, Controlled Trial' (2006) Journal of Pediatric Psychology Vol 32(3), p283.
Morrell and Cortina-Borja, 'The Developmental Change in Strategies Parents Employ to Settle Young Children to Sleep, and their Relationship to Infant Sleeping Problems, as Assessed by a New Questionnaire: the Parental Interactive Bedtime Behaviour Scale' (2002) Infant and Child Development Vol 11, p17.
Mosko, Richard and McKenna, 'Infant Arousals During Mother-Infant Bed Sharing: Implications for Infant Sleep and Sudden Infant Death Syndrome Research' (1997) Pediatrics Vol 100, p841.
Ostfeld et al, 'Sleep Environment, Positional, Lifestyle, and Demographic Characteristics Associated With Bed Sharing in Sudden Infant Death Syndrome Cases: A Population-Based Study' (2006) Pediatrics Vol 118, p2051.
Rickert and Johnson, 'Reducing nocturnal awakening and crying episodes in infants and young children. A comparison between scheduled awakenings and systematic ignoring.' (1988) Pediatrics Vol 81 p591.
Sadeh, 'Assessment and intervention for infant night waking: Parental reports and activity-based home monitoring' Journal of Consulting and Clinical Psychology, Vol 62, p63.
Scheers et al, 'Where Should Infants Sleep? A Comparison of Risk for Suffocation of Infants Sleeping in Cribs, Adult Beds, and Other Sleeping Locations', (2003) Paediatrics Vol 112, p883.
Scher et al, 'Sleep Difficulties in Infants at Risk for Developmental Delays: A Longitudinal Study' (2008) Journal of Pediatric Psychology Vol 33(4) p396.
Smaldone et al, 'Sleepless in America: Inadequate Sleep and Relationships to Health and Well-being of Our Nation's Children' (2007) Pediatrics Vol 119, pS29.
Task Force on Infant Sleep Position and Sudden Infant Death Syndrome, 'Changing Concepts of Sudden Infant Death Syndrome: Implications for Infant Sleeping Environment and Sleep Position' (2000) Pediatrics Vol 105, p650.
Taylor et al, 'Consistency in Infant Sleeping Arrangements and Mother-Infant Interaction' (2008) Infant Mental Health Journal Vol 29(2), p77.
Teti, Douglas et al 'Maternal Emotional Availability at Bedtime Predicts Infant Sleep Quality' (2010) Journal of Family Psychology Vol 24(3) p307.
Vennemann, 'Does Breastfeeding Reduce the Risk of Sudden Infant Death Syndrome?' (2009) Pediatrics Vol 123(3), pe407.
Worthman and Brown, 'Companionable Sleep: Social Regulation of Sleep and Cosleeping in Egyptian Families' (2007) Journal of Family Psychology, Vol 21(1), p124.