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Four Eye-Opening Things Science Tells us About Infant Sleep (Part 1 of 2)

One of the most muddled parenting topics is sleep. Infant and toddler sleep issues tend to be as controversial as they are challenging. In this guest post, scientist and author Alice Callahan, PhD discusses the findings from research on infant sleeping habits and how they stack up against her own practical experience as the mother of two children.

My first baby, Cee, was a yoga ball baby. If you’ve had one of these in your family, you know exactly what I mean. We discovered within the first week or two of her life that bouncing quieted her fussing and eventually put her to sleep, and so we adopted this method as part of her sleep routine.

Bouncing Cee to sleep worked well for a few months, but then it started taking longer and longer for her to fall asleep, and it was increasingly difficult to transfer her into her bed without her waking. She started waking more often during the night and struggling to go to sleep at all for naps. I tried other soothing methods, but by this time, anything but bouncing just seemed to make her more frustrated. It occurred to me that she was a yoga ball baby not because she was born that way but because we had trained her to sleep with bouncing, and bouncing only.

I finally stopped bouncing Cee, and after our usual routine of bath, milk, books, and lullaby, let her try going to sleep in her bed. She protested at first, but then she quickly showed us that she was quite capable of going to sleep on her own. Within a few days, she was finding a gentler transition to sleep – getting comfortable in her own way – and sleeping so much better.

My experience with Cee made me realize that we had underestimated her natural ability to sleep, and perhaps our attempts to help her sleep had interfered with her learning process. If we had another baby, could we do things differently, so that our baby’s sleep could develop more gradually?

Parenting is a constant learning process. Since Cee was a baby, I’ve learned a few things about infant sleep that helped this process go more smoothly when my son was born four years later.

First, I discovered Janet’s wonderful website, Magda Gerber‘s writing, and RIE. This gave me a simple framework that helped me to better understand my baby and find more calm confidence in parenting. When I started respecting my baby as a whole person, really observing her and letting her lead the way, and giving her safe and predictable routines, so much fell into place from there.

Second, as someone trained as a research scientist, I started reading hundreds of studies on infant sleep (among other topics that worry new parents). Surely, I thought, science could help answer my questions about caring for babies. That research led to many posts on my blog, and eventually, my book, The Science of Mom (published in 2015 by Johns Hopkins University Press). Incidentally, what I learned from the science often coincided with RIE philosophy and Magda Gerber’s observations of babies from decades before this research was published.

1. How babies sleep is a combination of nature and nurture.

I have to say this at the very start, because I don’t want to imply that infant sleep is always simple or that there is a certain formula to good sleep for every baby. The truth is that nature – a baby’s unique genetic make-up – accounts for somewhere between about a quarter and a half of the variation in infant nighttime sleep patterns.1,2 Sleep comes easier to some babies and harder to others, and if your baby struggles with sleep, it doesn’t necessarily mean that you’re doing anything wrong.

On the other hand, this leaves a lot of room for the influence of nurture – the way we care for our babies and the sleep environment that we create for them. As a parent, I found this empowering, and I wanted to know how I could nurture good sleep in my baby.

One of the ways that we influence our babies’ sleep patterns is through our attitudes and beliefs about infant sleep. These were measured in an Israeli study that surveyed 85 women beginning in pregnancy and when their babies were 1, 6, and 12 months old.3 The study also evaluated the babies’ sleep, allowing the researchers to see correlations between parenting philosophies and infant sleep patterns.

All of these mothers were caring and responsive, but their beliefs about infant sleep fell along a spectrum. Beginning in pregnancy, some mothers tended to interpret a waking baby as a distressed baby who always needed help from a caregiver. These mothers ended up taking a more active role in soothing their babies to sleep, and their babies also ended up waking more during the night in infancy.

Other pregnant mothers in the study believed that babies were capable of sleeping and that they didn’t always need help from a parent to sleep. These mothers were more likely to end up letting their babies settle on their own, and their babies ended up waking less during the night. A follow-up study found that mothers’ sleep philosophies at 12 months also impacted how their children slept at four years of age.4

These studies show that if we believe that our babies can sleep without our help, then they’re more likely to do so. I took this to heart, and my beliefs about sleep shifted significantly between the births of my yoga ball daughter and my son. With my son, I thought of him as capable of sleeping from the start, which brings me to my next point…

2. Babies know how to sleep, and learning to sleep is part of their normal development.

Newborn babies sleep a lot, and of course, they slept in utero, too. For the first week or two outside of the womb, babies often fall to sleep easily while feeding or snuggled in our arms, or they’ll drift off on their own after staring at the ceiling fan for a while.

Gradually, as they become more aware and stimulated by the world around them, they often struggle more with falling to sleep and staying asleep. The challenge to parents is to support our babies through this normal developmental course and let them continue to practice and adapt their sleep skills.

In a fascinating study published in 2015, 101 London infants were video-recorded through one night at 5 weeks and 3 months of age.5 All of the infants woke during the night, but at both ages, about one quarter of the babies resettled during the night without the help of their parents. Most didn’t cry upon waking, and the rest fussed or cried for an average of about one minute before going back to sleep. The published study included a sweet 3-minute video example of a 3-month-old baby resettling during the night. An earlier study found that about half of 3-month-olds resettled in the middle of the night without help from a parent.6

Although not all of the babies in these studies were observed to resettle themselves, it shows that the possibility is there, and more babies might resettle if given a few minutes to try. Another study showed that when parents gave their 3-month-olds a few minutes to try to go back to sleep on their own after a night waking, they were more likely to be sleeping through the night at 12 months of age.7

Between the 5-week and 3-month measurements, the London study also found that there was a clear developmental progression in lengthening sleep periods.5 By 3 months of age, 68% of babies were sleeping (or self-settling) for at least a 5-hour stretch during the night, and this was just as likely with exclusively breastfed babies as with formula-fed babies. There was also a big increase in the number of infants that sucked on their fingers or hands during sleep (from 18% at 5 weeks to 62% at 3 months). These babies were finding that a little comfort was as close as their own hands.

There is so much happening in sleep development during the first few months. It’s worthwhile for us to slow down and observe our babies with curiosity to see what they are capable of. As their sleep physiology develops, some babies will need more support than others, but we can start from a place of believing our babies are capable of sleeping and finding ways to let them practice this skill.

3. Babies who are able to go to sleep on their own are more likely to be able to resettle themselves during the night.

This is one of the most consistent findings in infant sleep research. Babies who fall to sleep on their own at the beginning of the night tend to sleep better during the night, whereas more active soothing from a parent at bedtime is associated with more disrupted sleep during the night. All babies wake several times during the night, but those that know how to go to sleep on their own are more likely to be able to comfortably resettle in the night without crying for help from a caregiver. This has been shown in studies from around the world, including the United States and Canada, Thailand, the U.K., and in a cross-cultural survey of more than 29,000 babies from 17 different countries.6,8–13

4. You can nurture both autonomous sleep and secure attachment in your baby.

Each of us tasked with caring for a baby is building a relationship with that baby through our daily – and nightly – interactions. We want that relationship to be one of secure attachment. We want our babies to know that we are here to care for them, that we will listen to what they are telling us and respond appropriately to meet their needs. This secure attachment gives babies the confidence to explore and learn, knowing that they can always come back to us for support if needed.

There is a tendency to believe that secure attachment depends on constant physical presence and soothing, but this belief is not supported by science. Several studies have found that babies who settled to sleep on their own were just as likely to be securely attached as those who were actively soothed to sleep.14,15

In addition, running to hush a crying baby as quickly as possible won’t increase secure attachment.16As these authors put it, “…mothers of securely and insecurely attached infants are not different in terms of how frequently they respond to their infants’ signaled awakenings; they are different in that, when they respond, mothers of securely attached infants are more likely to respond sensitively and consistently.”14 Being sensitive to your baby’s needs (including the need to sleep) and being consistent (including when you make changes to your sleep routine) are vital to healthy attachment, and you can absolutely be both while encouraging independent sleep for your baby.

(How did I put this science into practice with my son? I’ll tell you more about that in Part 2: How I Helped My Baby Learn to Sleep)

Alice Callahan is the author of The Science of Mom: A Research-Based Guide to Your Baby’s First Year. You can find more of her work on her blog, Science of Mom, and her Facebook page.

(Thumbnail photo by Lori Cole. Baby wrapped in blanket photo by Alice Callahan.)

Alice (and I) welcome your comments and questions!


  1. Touchette, E. et al. Genetic and Environmental Influences on Daytime and Nighttime Sleep Duration in Early Childhood. Pediatrics 131, e1874–e1880 (2013).

  2. Fisher, A., van Jaarsveld, C. H. M., Llewellyn, C. H. & Wardle, J. Genetic and environmental influences on infant sleep. Pediatrics 129, 1091–1096 (2012).

  3. Tikotzky, L. & Sadeh, A. Maternal Sleep-Related Cognitions and Infant Sleep: A Longitudinal Study From Pregnancy Through the 1st Year. Child Dev. 80, 860–874 (2009).

  4. Tikotzky, L. & Shaashua, L. Infant sleep and early parental sleep-related cognitions predict sleep in pre-school children. Sleep Med. 13, 185–192 (2012).

  5. St James-Roberts, I., Roberts, M., Hovish, K. & Owen, C. Video Evidence That London Infants Can Resettle Themselves Back to Sleep After Waking in the Night, as well as Sleep for Long Periods, by 3 Months of Age. J. Dev. Behav. Pediatr. 36, 324–329 (2015).

  6. Anders, T. F., Halpern, L. F. & Hua, J. Sleeping through the night: a developmental perspective. Pediatrics 90, 554–60 (1992).

  7. Burnham, M. M., Goodlin-Jones, B. L., Gaylor, E. E. & Anders, T. F. Nighttime sleep-wake patterns and self-soothing from birth to one year of age: a longitudinal intervention study. J. Child Psychol. Psychiatry 43, 713–25 (2002).

  8. Mindell, J. A., Sadeh, A., Kohyama, J. & How, T. H. Parental behaviors and sleep outcomes in infants and toddlers: a cross-cultural comparison. Sleep Med. 11, 393–9 (2010).

  9. Sadeh, A., Mindell, J. A., Luedtke, K. & Wiegand, B. Sleep and sleep ecology in the first 3 years: a web-based study. J. Sleep Res. 18, 60–73 (2009).

  10. Touchette, É. et al. Factors associated with fragmented sleep at night across early childhood. Arch. Pediatr. Adolesc. Med. 159, 242 (2005).

  11. Anuntaseree, W. et al. Night waking in Thai infants at 3 months of age: Association between parental practices and infant sleep. Sleep Med. 9, 564–571 (2008).

  12. Morrell, J. & Cortina-Borja, M. 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. Infant Child Dev. 11, 17–41 (2002).

  13. Adair, R., Bauchner, H., Philipp, B., Levenson, S. & Zuckerman, B. Night waking during infancy: role of parental presence at bedtime. Pediatrics 87, 500–504 (1991).

  14. Higley, E. & Dozier, M. Nighttime maternal responsiveness and infant attachment at one year. Attach. Hum. Dev. 11, 347–363 (2009).

  15. Scher, A. & Asher, R. Is attachment security related to sleep–wake regulation?: Mothers’ reports and objective sleep recordings. Infant Behav. Dev. 27, 288–302 (2004).

  16. van IJzendoorn, M. H. & Hubbard, F. O. Are infant crying and maternal responsiveness during the first year related to infant-mother attachment at 15 months? Attach. Hum. Dev.2, 371–391 (2000).

#SelfSoothe #newborndevelopement #infantsleep

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