Baby sleep

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This text is part of: "Science of sleep" by Piotr Wozniak (2017)

How to make babies sleep well?

People often say "I slept like a baby". A joke says that it means that you kept waking up every 2 hours to scream. Indeed, babies tend to wake up in the night, and seem unhappy unless immediately soothed with mama's breast. This seems unnatural, unnecessary, and worrying. And yet babies have been designed to wake up many times during the night to feed.

The net is jam-packed with an assortment of advice from and for young parents who seek good sleep for their babies and for themselves. A great deal of that advice is based on myth and/or pseudoscience. If the advice includes the word "train" or "schedule", you need to triple your skepticism! Even world renowned pediatricians overemphasize the "routine" over the actual natural sleep mechanisms. As much as adult's, baby sleep is ruled by homeostatic and circadian mechanisms, and any attempt to override those is futile and potentially harmful. All routines such as rocking the baby, quiet room, feeding, quiet talking, music, etc. are welcome as long as they are not attempts to enforce a sleeping schedule on a baby. These routines are little more efficient in inducing sleep as all the grandma's advice against insomnia. Neither homeostatic nor circadian mechanism is trainable (beyond natural phase shifts, etc.). Babies should sleep on demand (ad libitum), i.e. only then when they are sleepy and want to sleep. Nevertheless, understanding their circadian patterns can be very helpful in assisting the routine. As baby sleep is more complex than adult sleep, you can use SleepChart to see through the chaos. This can help as guidance. Nevertheless, observing the symptoms of sleepiness is the oldest and the best practice.

Some moms claim proudly "my baby sleeps through the night". However, when actual sleep logs or hypnograms are analyzed, this appears not to be true. A great proportion of parents will go to any length to make their baby sleep through the night. All too often, parental convenience and comfort take precedence to baby's health. Many pediatricians are pretty ignorant in reference to the rules of chronobiology, which is not prominent enough in school curricula. Some acclaimed methods are plain scary.

The cry-it-out method must have been inspired by Pavlov's methods in conditioning dogs. There is little doubt that prolonged crying and stress will inhibit baby's development. For example, if prolonged crying correlates with later cognitive deficits, it is, at least to a degree, related to the impact of stress on development (Rao et al. 2004[1]). In the end, Ferber's method seems to serve the parent, not the child. No parent's heart should stand baby's cry, esp. that it is entirely unnecessary.

Sleeping throughout the night

It takes roughly 1-2 months for the baby sleep to align into a rudimentary circadian pattern.

In the first weeks, a newborn baby does not see much difference between the night and the day!

Consolidation of the fasting-associated wakefulness precedes that of the breastfeeding rhythm due to high feeding demands in the first few weeks of life (Odaa et al. 2008[2]).

An exemplary chart of homeostatic and circadian sleep preferences in the first 2 months of life

Figure: An exemplary circadian graph of homeostatic and circadian sleep preferences in the first 2 months of life. The average length of unconsolidated sleep episode (red line, left vertical number line) varies from 0.5 hour at 4 pm to 1.5 hours at 9 pm. There is a slight circadian preference for initiating sleep in the early evening hours (6.2% at 5 pm)(blue line, right vertical number line) as opposed to the morning (below 3% at 6-7 am). Using various sleep consolidation methods (i.e. methods for adding up episodes that follow in a short succession), the preference for the evening sleep may be shown to be more pronounced. The preference for night sleep keeps increasing in the first months of life in line with brain development

Your baby may redistribute its sleep episodes equally in the day and in the night. For an ever-sleepy mother, it can lead to the illusion that the baby stubbornly tends to sleep during the day, and just keeps crying throughout the night. No wonder that many moms keep asking: What am I doing wrong?, How can I make my baby sleep in the night? The short answer is: Nothing! (unless there is an organic cause disrupting sleep)! Sleep in short 1-4h bursts throughout the 24 hour period is normal in newborns, and nothing can be done about it! Moreover, whatever parents try to accomplish that goal is likely to be harmful for the baby.

Efforts to make a baby sleep through the night in its first months are a waste of time, and may even be harmful!

In the exemplary sleep log below, we can see how the chaos of the first months slowly consolidates into a sleep pattern with a major nocturnal sleep episode and several naps during the day. Around five months of age, a pretty consistent pattern emerges with two daytime naps on most of days. Finally, at around one year old, an adult-like biphasic rhythm develops. The breakthrough usually comes when parents, unaware of the consolidation process, realize that the baby does not want to take the early nap and soon put the kid to sleep only once per day. Multiple naps during the day, at this stage, are often a result of health problems, missing some of the night sleep (e.g. due to early waking for infant nursery), bad "baby sleep management" (i.e. mostly not responding to baby sleep signals), or temporary variations resulting from lifestyle changes (e.g. travel, exhausting play, meeting people, etc.). Unless the infant clearly demands multiple naps, a single siesta nap after passing the age of 12-16 months is probably a pretty safe bet. Some parents try to push the kid to stay awake throughout the day to ensure a more solid nighttime sleep. However, sticking to child's natural preference is always a safer option.

An exemplary free running sleep log in the first year of life

An exemplary free running sleep log in the first year of life

Interestingly, in the presented graph there are 3 months, in which the infant tends to go to sleep very late. Such a sleep pattern may be a worrying prelude to future developmental, psychological or sleep problems. However, in this case it might have as well been explained by lesser resetting impact of morning sunlight in winter months. Spectral analysis of sleep in the first months shows that baby circadian cycle might possibly be quadriphasic with constituent frequencies getting damped over time to develop a typical biphasic rhythm with a major nighttime and a minor daytime crests.

For another example of the crystallization of the circadian cycle, see this one father's effort to map the regularities in his baby's sleep. This particular chart begins at a stage when the baby is primarily nocturnal, but still diurnally polyphasic (4th month). Around the 10th month, daytime napping consolidates showing a quadriphasic mode with nocturnal "naps" consolidated into a single long night-time sleep episode. Finally, around the 16th month, the child develops a crisp biphasic pattern. That transition to the biphasic mode might have been delayed somewhat by parental decisions that often determine infant's sleep slots.

Parental decisions as to the timing of sleep will largely determine the baby sleep pattern. This is why the understanding of the natural development of the circadian cycle and responding to natural baby sleep signals is vital for healthy baby sleep!

Development of a healthy circadian cycle

There are two main factors that will affect the development of a healthy circadian pattern in a baby:

  1. Exposure to the natural 24-hour cycle of daylight and darkness, and all the associated daily routines.
  2. Exposure to mother's circadian routines, amplified by co-sleeping

In many animals, the development and the initial entrainment of the circadian cycle is primarily dependent on the interaction with the feeding mother (Rivkees et al. 1988[3]). Co-sleeping should assist in the development of a healthy circadian cycle. Mother's presence in bed as well as breastfeeding can both act as powerful cues. They act as both PRC-related and PRC-independent zeitgebers (see: How do we fall asleep?). This means that co-sleeping will affect the sleep phase as well as the degree of nocturnal awakening and total sleep. In addition to sensory cues, breastfeeding plays also a hormonal role as the circadian cycle of tryptophan in breast milk correlates with the levels of melatonin in the child's blood (as evidenced by 6-sulfatoxymelatonin in urine; Cubero et al. 2005[4]). This naturally calls into question the practise of collecting expressed milk for later use. The development of a healthy sleep-wake cycle will naturally also depend on the fact whether the mom herself applies the adequate principles of sleep hygiene. Millions of children are forced to sleep alone in their cots. This practise is so widespread in the industrialized nations that we may safely conclude that it does not irreversibly ruin the baby's circadian cycle, but, theoretically, it might underlie the epidemic of sleep disorders in modern societies.

In addition to the postnatal period, mother's circadian cycles exert their impact on the baby's brain already in pregnancy. This adds to the utmost importance of sleep hygiene in gestation.

It remains controversial if nighttime exposure to artificial light can slow down or disrupt the process of the circadian cycle development. Research on the impact of light on the development of the SCN suggests that it is possible to change rhythmicity or sensitivity to light of the body clock. The changes occurring in the course of development might affect the properties of the clock for a lifetime. However, it is also possible that lifestyle can reverse or magnify those changes. The development of the SCN has been studied in many animals and results differ. For example, rat SCN periodicity develops in utero (Altman and Bayer 1978[5]), while the sleep-wake cycle in the SCN in an opossum develops in the first 3 postnatal weeks (Rivkees et al. 1988[3]). The shape of the phase response curve, which lays at the root of sleep phase disorders, may actually be influenced by illumination conditions during the development, at least in cockroaches (Page 1991[6]). Whatever the impact of light and locomotor activity in babies, until we know more, we should always aim at minimizing nighttime exposure to artificial light, and to minimize its luminance.

Despite the usual claims to the contrary, nighttime play might actually accelerate the return to sleep as long as the emphasis is put on physical as opposed to the emotional. However, as motor activity is also able to phase shift the circadian cycle, nighttime play on demand should probably be minimized.

Mothers can help the development of a healthy sleep control system by: (1) breastfeeding, (2) co-sleeping and (3) avoiding artificial light

For more more see: Polyphasic sleep in babies

Co-sleeping as a circadian solution

The process of maturing the circadian rhythm is neural and largely beyond parental control. However, the entrainment of mom's and baby's cycles is essential, and may determine the ultimate outcome of the process. Newborns are driven to sleep homeostatically, and woken up primarily by their feeding needs. Factors such as temperature, hunger, play, lighting, social interaction, etc. only add complexity to the picture. With a number of hard-to-predict factors that affect sleep needs, babies should always sleep on demand. If they want to play, the play should not be denied. All scheduling in their life should be done around their sleep. This basically means there are only two practicable solutions to newborn's good sleep:

  • Recommended (McKenna et al. 2005[7]): Mom and the baby sleep together. A mom needs to learn to adapt to periodic breastfeeding throughout the night. Mom's sleep will suffer a bit. However, with a bit of practice, breastfeeding can be minimally disruptive, and actually act as a soporific for both the baby and the mom. In other words, after a short breastfeeding session, both the mom and the baby should quickly fall asleep contented with the job well-done. Even though the development of the circadian cycle should proceed regardless, co-sleeping should assist that vital biological process. Baby safety issues related to sleeping together must be addressed beforehand (you can google for that in minutes: example). Even a strong one year old can be suffocated easily. If you believe your power baby will scream or wriggle, it is not true! When its chest is compressed or breathing passages get obstructed, a baby will nearly instantly lose strength and be unable to defend itself! This is why safety is paramount. For a healthy and vigilant mother, statistics are good. A bit of anxiety at the start is unavoidable and perhaps good to develop healthy and safe sleeping habits. Psychologists, behaviorists and all open-minded pediatricians will all admit that the night-time bonding is great for baby's brain development. Perfect formula for both the mom and the child.
  • Emergency: Parental care in shifts with the help of breast milk. It may happen that for health reasons, the mom and the baby should sleep separately for a while. In such cases both parents can still get excellent sleep if they adapt to a variant of shift-work with the help of chronotherapy. For example, one of the parents chronobiologically adapts to sleeping in the 7 pm - 1 am bracket, while the other takes the 1 am - 7 am shift. In the period when the mom is asleep, breast milk, extracted in advance (or formula) can be used instead of breastfeeding to avoid major disruptions to mom's sleep (remember that milk properties also change along the sleep-wake cycle). If that solution is not feasible for any reason parents will probably need to choose between:
  1. their own good sleep, and
  2. employing a nighttime nanny.

Needless to say, baby's sleep should never be at stake here. Sleep is vital for adult health. However, for a baby it is literally a matter of life and death as sleep disruption will have an effect on many causes of newborn mortality.

Best timing for feeding

Unless specifically indicated by a qualified pediatrician for specific health reasons, feeding "on the clock" should be banished.

Never wake your baby up for feeding! Feeding on demand is baby's best option!

One of the cardinal sins of parenthood is overfeeding! Here are two scenarios I saw in real life:

  • It is easy to observe that after a hefty dose of formula sucked down in a hurry, babies get drowsy for reasons that have little to do with actual sleepiness. It may then be tempting to feed the baby to sleep. Such a practice is bad for baby's health and will not help him or her sleep overnight. It may only assist a short-lasting sleep that will clear the homeostatic sleepiness and make baby even less sleepy than before feeding.
  • Another reason for overfeeding is mom's convenience. In hope of getting some more uninterrupted sleep, mom will feed a baby extra formula before the night or during a nighttime feeding session. Again, parent's convenience may be harmful for the child!

Child's own bed

The American Academy of Pediatrics has amazingly come up against co-sleeping! Many moms will swear their babies can sleep alone in a cot without any distress. And yet most behaviorists and anthropologists will agree: the mom and the baby should sleep in close contact as it has been practised by the human race for millennia, and by nesting mammals for millions of years. There could be exceptions on health or safety grounds. However, for an average mom, sleeping with the baby should be a pleasure, a privilege and a duty. The young mom only needs to read about basic safety measures. For a baby, sleeping with the mom should be a basic human right! Many pediatricians, nurses, midwives and "old school" grandmas will still insist that the baby should sleep it its own bed for safety, discipline or convenience reasons. You may hear a medical professional advise: "Don't reward the baby! You are making a rod for your own back". This is very surprising in the light of the fact that baby reward system is pretty well tuned to satisfying its biological needs. An average adult with a number of control mechanisms messed up by the modern lifestyle should often be denied its rewards (a fat doughnut, a morning shot of whiskey, etc.). However, all natural rewards should be considered biologically advantageous for a baby. As for the safety issues, babies do die when sleeping with moms in soft beds, due to alcohol, etc. They do so too when sleeping alone. Simple preventive measures dramatically reduce the risks of the dreaded mishap. The idea that we should train up a child to sleep alone from birth is hard to uproot. One needs to look closely at the biology of breastfeeding and baby sleep to quickly realize that training up at that stage amounts to little less than cruelty (except for cases and moments where the baby does not seem to object sleeping in a cot or in mom's absence from the common bed). A little baby is basically a feeding, growing and learning machine. All its inborn reflexes are targeted at ensuring safety, growth, and brain development. The reflexes involved in rooting, sucking, and breastfeeding belong to the strongest drives in a little baby. A whole series of brain centers is involved and there is a close relationship between these centers, sleep centers, and the sense of well-being and pleasure. Even though the complexity of the mechanisms involved is far from being revealed to our understanding, denying a baby mom's breast and closeness is bound to have long-term developmental consequences. Metaphorically, you could try to put yourself in baby's boots by trying to sleep naked on cold concrete with horror movies blasting loud throughout the night. I might be overly dramatic here. If a baby goes to sleep on its own without much ado, its proximity craving is definitely not as powerful as described here. However, when a baby's growth is at stake, you should always err on the safe side. This is why it makes sense to assume the worst case scenario. I would not be surprised, if over time researchers discovered a need to extend the two-process model of sleep propensity in babies by a factor involved in breastfeeding. It has been shown that a tit is a soporific. I would not be surprised if it worked as an integral contributor to baby's homeostatic sleep propensity, or even a homeostatic trigger, esp. at time where the circadian cycle is not yet fully expressed. Needless to say, babies need sleep even more than adults. The degree of neural growth, network remodelling and learning in a young brain is staggering. Both NREM and REM sleep components are essential in that process. Changing the sleep structure will affect neurogenesis (Stryker et al. 2001[8]). In other words, any form of stress before or during sleep will affect baby's brain growth. This is why baby's sleep should be the zone of highest protection. Training up to sleep alone can wait. Piglets weaned early have been shown to suffer damage to their hippocampus that results in personality changes, fear of exploration, and low stress tolerance.

Many parents oppose attachment parenting as too expensive timewise. It is hard to argue with someone who needs to choose between feeding the family and behavioristically correct approaches. Here again, modern lifestyle encroaches on human biology in a vicious cycle of long-term consequences in which babies brought up using an assembly line approach are emotionally and intellectually less likely to stand up to challenges of reconciling technological and societal progress with the needs of the human body and brain. For more see: Is sleeping with my baby safe? (McKenna 1995[9]) and The Science of Attachment Parenting.

What about the mom?

Is co-sleeping good for the mom? I believe everyone should taste the blessings of free running sleep. However, some of my good sleep advocacy needs to take an exception here as mom's health takes a secondary importance where baby sleep is at stake. Every mother is equipped with hidden or overt instincts that should make the experience of co-sleeping pleasurable. Naturally, in the modern world, stress, mobile phones, TV, Internet, rat race, and other factors can make it very hard. If a mom claims "I hate breastfeeding", or "I cannot sleep with my baby", she should start from a thorough examination of her own life. Breastfeeding and co-sleeping can be very rewarding if the household is sufficiently sheltered from the storms raging outdoors.

Why babies sleep so much?

Do babies sleep so much because they're learning so much or are they learning so much because they are getting so much sleep? Babies sleep so much because their brains have been designed to do so in the first months of their life. They do learn a lot, and learning does increase the demand for sleep, but this is not the main regulatory factor. Sleep control systems in babies simply work differently, and you probably would not be able to make babies sleep less by making them learn less. On the other hand, long bouts of sleep are used to reorganize neural networks in the brain. In short, sleep helps learning, learning induces sleep, but the whole sleep sequence is a direct outcome of genetically programmed properties of a young sleep control system. Considering the fact that babies spend around 50% of their sleep time in the REM phase (as compared to around 20% for adults), one of the theories says that even when babies do not learn much during the day while exploring their surroundings, that function is filled up by the exploratory function of the REM sleep which helps them discover new properties and rules in things they have learned thus far.

You will often hear that newborns sleep most of the time. Actual measurements may show that babies are more likely to sleep through just half of their days, while spending only a small proportion of that in deeper stages of NREM sleep.

An exemplary SleepChart log of sleep in the first month of life

An exemplary SleepChart log of sleep in the first month of life. Sum total of all sleep blocks is displayed on the right and averages to slightly above 10 hours per day with substantial day-to-day variations reflecting the impact of rich homeostatic input changes such as a walk, family visit, diaper rash episode, formula supplementation, etc.

Conclusion: Perfect formula for baby sleep

Babies sleep best if they sleep on demand and if they are fed on demand! All forms of artificial intervention in those homeostatically-regulated patterns should be considered potentially harmful. It is helpful to spot regularities and pay extra attention to baby signals at his or her preferred feeding and sleep times, however, it is the baby's needs that should determine the actual timing. As sleep is vital for the development of neural structures in the growing brain (Stryker et al. 2001[8]), any form of intervention and artificial control should be considered potentially harmful in the long-term.

If you want your baby to be smart and healthy, let it play on demand, feed on demand, and sleep on demand


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