Baby sleep patterns:
A guide for the science-minded
© 2008 - 2014 Gwen Dewar, Ph.D., all rights reserved
This article covers the science of baby sleep patterns. Here you’ll find information on
- How and when babies adapt to natural cycles of day and night
- Baby sleep states and sleep cycles
- Factors that affect arousal (how easily your baby awakens from sleep)
- The myth of “sleeping through the night”
- The ways that babies fall asleep (a cross-cultural review)
- Stimulation, over-stimulation, and sleep problems
- How your baby’s temperament may affect her sleep patterns, and
- Developmental milestones and changes that can disrupt baby sleep patterns.
I focus on babies aged 1 month – 2 years. If you are interested in newborns, see my article on
baby sleep patterns during the first 4 weeks of life.
If you’re looking for information about how many hours babies should sleep, see my article on
baby sleep requirements.
And for detailed information about sleep disturbances, see my article on
infant sleep problems.
Why baby sleep patterns are different
Young babies are notorious for sleeping and waking at awkward
times. In part, this is because they haven’t yet developed mature
At birth, baby sleep patterns aren’t cued to the natural cycle of
day and night. It can take several months before babies become fully
adapted to the 24-hour day. Until that happens, babies are unlikely to
“settle” for lengthy periods during the night.
(For tips on how you can help your baby make this transition, see
"How to help babies adapt to the 24-hour day" in my article on
But there is another, more fundamental reason for the awkward timing of
baby sleep. Babies sleep is just plain different. Compared to adults,
babies spend much less time in deep sleep. And babies’ sleep cycles are
As a result, babies are much more easily awakened.
Sleep states and sleep cycles: The basis of baby sleep patterns
To better understand how baby sleep patterns differ from your own, it helps to review what happens when you sleep.
When adults fall asleep, we pass through a series of sleep
stages, including bouts of deep (“slow wave”) sleep, and, finally, REM
(rapid eye movement) sleep.
REM sleep is well-known for its association
with dreaming. It is also notable for its pattern of brain activity,
which resembles that of the waking brain. Some systems of the body are
pretty active, too. Although the skeletal muscles become temporarily
paralyzed, the eyes dart around beneath the eyelids, and breathing and
heart rates become irregular.
People are least like to awaken while in deep sleep. They are more likely to awaken from REM sleep.
For the average adult, a single sleep cycle--beginning with stage
1 sleep and ending with REM sleep--takes about 90-100 minutes. At the
end of a cycle, the sleeper will either awaken or pass back into an
earlier sleep stage and repeat the cycle.
As we’ll see, baby sleep patterns are very different.
The quirky nature of baby sleep states
Compared to adult sleep patterns, baby sleep patterns are a simple
affair. Babies have two sleep states--active and quiet--and their sleep
cycles are short, only 50-60 minutes for the first nine months (Jenni et
Active sleep comes first. It's the baby-equivalent of REM sleep, and, like adults in REM, babies
engaged in active sleep awaken more easily (Anders 1979; McNamara et al
2002). Babies in active sleep exhibit fluttering eyelids; relatively rapid, irregular breathing; occasional
body movements; and vocalizations (grunts or brief cries).
About half way through the sleep cycle, babies pass from
active sleep to quiet sleep. As its name suggests, quiet sleep is
characterized by slower, more rhythmic breathing, little movement, and
no eyelid fluttering.
While in quiet sleep, babies are less likely to be awakened by
noise and other disturbances—including a sudden reduction in the oxygen
supply (Parslow et al 2003).
Quiet sleep represents the end of the baby’s sleep cycle. When
it’s over, babies either begin the cycle again (re-entering active
sleep) or they wake up.
As babies mature, quiet sleep begins to differentiate into
distinct NREM stages. In addition, their sleep cycles lengthen, and they
spend proportionately less time in active, or REM, sleep.
But change is gradual, and it takes several years for children’s
sleep patterns to resemble those of adults. Although NREM sleep stages
emerge by 6 months, sleep cycles don’t reach the 90-100 mark until
children are school-aged (Jenni and Carskadon 2005). And, throughout
early childhood, kids spend a lot time in REM sleep. Whereas adults
spend only 20% of sleep time in REM sleep, REM represents 50% of sleep
time in newborns and 30% of sleep time in three year olds (Anders 1979).
Sleep states and baby sleep patterns: The practical implications
As we've seen, babies cycle rather quickly, back and forth, between active and quiet sleep. This means:
• Compared to adults and older children, babies are light sleepers. They spend proportionally more time in active sleep.
• Babies are especially easily awakened for 25 minutes (or more)
after first falling asleep. That’s why it can be so hard to move a
sleeping baby without waking him.
• Babies may experience arousals every 50 minutes or so. If
you’re lucky, these arousals are only partial and your baby goes back to
sleep without a fuss. If you’re unlucky, your baby becomes fully
aroused—and let’s you know about it.
If you’re a sleepless parent, active sleep might sound like a bum
deal. But it’s likely that active sleep is important for a baby’s brain
development (Siegel 2005).
And it’s also possible that active sleep is “safer” sleep, at
least for babies who aren't predisposed to SIDS. Experimental research
suggests that healthy infants are more likely to wake up if they
experience breathing problems during active sleep than during quiet
sleep (Parslow et al 2003).
For some babies--those predisposed to SIDS--active sleep is
associated with higher risk. A study of babies who later died of SIDS
found that these infants were less likely than healthy babies to arouse
from active sleep (Kato et al 2003). Active sleep is associated with
more frequent episodes of heart rate irregularities and sleep apnea,
conditions that are potentially life-threatening if a baby doesn't wake
But the main point is this. Babies who are aroused more easily are at a lower risk for
SIDS, or sudden infant death syndrome
(Horne et al 2002b).
Nonetheless, some babies are aroused more easily than others.
Here are some environmental factors that affect baby sleep patterns of
Factors that affect arousal—and risk for SIDS
Studies suggest that babies are HARDER to arouse (and therefore at greater risk of SIDS) under the following conditions:
• They live with a smoker (Horne et al 2004a)
• They sleep on their stomachs (Horne et al 2001; Kato et al 2006)
• They are sleep-deprived (Franco et al 2004)
• They are recovering from an infection (Horne et al 2002)
• Their faces are covered by bedclothes (Franco et al 2002; Blair et al 2008)
• Room temperature is high (e.g., temperatures of 28C/82F are
associated with fewer arousals than are temperatures of 24C/75F—-Franco
et al 2001)
Studies suggest that babies are aroused more easily (and therefore at lower risk of SIDS) under the following conditions:
• They sleep in the supine position (i.e., on their backs; Horne et al 2001).
• They sleep in the same room as their mothers
(Mosko et al 1997; Mao et al 2004). But note that bed-sharing -- as practiced by
Western populations -- is linked with a higher risk of SIDS for young
infants. See this article about
bed sharing safety
for the details.
• They are breastfed. In experiments, breastfed babies were aroused more easily than were
formula-fed babies (Horne et al 2004b; Franco et al 2000).
• They use pacifiers (Franco et al 2000).
What about sleeping through the night?
If you consider that baby sleep patterns are characterized by short,
50-60 minute sleep cycles, you may wonder how it’s possible for babies
to “sleep through the night.”
The answer is that “sleeping through the night” is a myth.
A variety of anthropological, historical, and clinical evidence
suggests that adults are not designed to sleep through the night. Let
With their short sleep cycles, babies experience more
opportunities for arousal. And they have smaller stomachs, which means
they need to eat more frequently than adults do.
So when some parents boast that their baby is sleeping through
the night, what they’re really saying is that they are not aware of
their baby’s night-time arousals. Their baby, in other words, doesn’t
make enough noise to awaken them.
How long does this blessed state last? Depending on the age of
the baby, maybe no more than 5 hours (e.g., Pinilla and Birch 1993).
Where and how babies fall asleep: Cross-cultural baby sleep patterns
Many Western baby “sleep trainers” warn parents against letting their
babies fall asleep at the breast or in their parents’ arms. They also
warn against rocking or singing babies to sleep. Babies, the sleep
trainers argue, must learn to fall asleep alone. They should be trained
to “self-soothe,” even if this means babies cry themselves to sleep.
There are limits to these recommendations. For instance, sleep
scientists warn that the “cry it out” approach must be carefully
monitored and should not be attempted on infants less than 6 months of
age (France and Blampied 1999; Owens et al 1999). But in general, the
sleep trainers believe that parents should encourage babies to fall
asleep by themselves.
From an anthropological standpoint, this is an unusual scenario.
Throughout human evolution, babies have fallen asleep while they nursed.
They have fallen asleep while they were held or carried—often in the
midst of the daily bustle. And they have fallen asleep lying in bed next
to their mothers.
Consider this sample of traditional baby sleep patterns:
• From Africa to the Arctic to the Americas, modern-day
hunter-gatherers keep their babies in close, physical contact throughout
the day, and mothers typically sleep with them at night. Babies
frequently fall asleep while breastfeeding and experiencing skin-to-skin
contact (Konner 2005).
• In Bali, babies sleep with their mothers until age three.
During the day, they are carried in slings as their mothers go about
their daily work. Babies may fall asleep in the sling, and, if mothers
must put their babies down, they are encouraged to give them to someone
else to hold (Diener 2000).
• Among the Beng, village farmers living in the Cote D’Ivoire,
babies spend their days on someone’s back—either the mother or a
designated baby carrier. Carrying a baby in this way is considered a
good way to get babies to fall asleep (Gottlieb 2000).
• In Japan, family members have traditionally slept in the same
room, and many babies sleep in their parents’ beds (Fukumizu et al
2005). Where babies sleep in their own beds, parents often lie with
babies until they fall asleep (Moore et al 1957).
• In Italy, babies are not usually assigned a special bedtime,
and often fall asleep before their parents put them to bed. For the
first year of life, a baby often sleeps in his parents’ bedroom (New et
• Mayan babies share their mothers’ beds—and may breastfeed during the night—until they are 2-3 years old (Morelli et al 1992).
• Among the Ifaluk of the South Pacific, babies sleep alongside
their parents each night. This continues until they are about three
years old. During the day, babies may be rocked to sleep (Le 2000).
• In Turkey, babies are often permitted to fall asleep while they
nurse. Babies are also swaddled and rocked to sleep in their cradles
Even in the United States—where sleep training is widely
touted—it’s not clear how many parents are following the advice of baby
trainers. In a recent study that tracked children from 6 months to 4
years of age, most parents soothed their babies to sleep (Gaylor et al
So why do Western sleep experts promote solitary sleeping for
One stated reason is that it encourages emotional independence
However, as anthropologist James McKenna has pointed out, there
is no research to support the idea that falling asleep alone makes
children more independent (McKenna and McDade 2005). Indeed, the little
research that does exist on behavioral outcomes suggests that children
who co-sleep with their parents develop higher self-esteem (Okami et al
A more valid argument for the solitary sleeping regimen is that
it promotes quieter babies. Studies confirm that babies who fall asleep
by themselves are more likely to go back to sleep by themselves when
they awaken in the middle of the night (e.g., Anders et al 1992). For
many parents, this can be an important advantage.
But for parents who are concerned about the possible adverse
effects of solitary sleep training--or who just prefer to soothe their
babies because it feels intuitively right--the promise of fewer night
wakings is not enough to change their minds.
And interestingly, parents who don’t expect their children to
fall asleep by themselves are less likely to report that their children
have sleep problems (Morelli et al 1992).
Indeed, parents living in co-sleeping cultures are often
disturbed to hear that some Western babies are left to sleep alone. To
them, the practice seems tantamount to child neglect (Morelli et al
Is the custom of solitary sleeping is bad for babies? Some
researchers and pediatricians speculate that a rigidly-imposed solitary
sleep regimen may stress children, damage parent-child relationships, or
cause sleep disturbances (Sears et al 2005; McKenna and McDade 2005).
Given that babies vary in their psychological and emotional needs, it
seems plausible that at least some babies will suffer problems if forced
to follow a solitary sleep regimen. But more research is needed to test
Meanwhile, the cross-cultural evidence suggests that babies
didn’t evolve to fall asleep by themselves. And studies of Western
babies show that most babies don’t fall asleep without parental soothing
(Gaylor et al 2005; Goodlin-Jones et al 2001).
Stimulation and baby sleep patterns
The total amount of time that babies spend sleeping may vary from
culture to culture. For instance, a study conducted in the 1990s
reported that 3-month old Dutch infants slept 2 hours more than did
American infants at the same age (Super et al 1996).
In part, such differences may reflect different attitudes about
stimulation. Whereas American parents feel it is their duty to fill
their babies’ days with developmentally stimulating experiences, Dutch
parents tend to emphasize rest and regularity (Super et al 1996). Babies
that receive lots of sensory stimulation during the day may have
greater difficulty falling and staying asleep.
Individual differences in baby sleep patterns
Not surprisingly, baby sleep patterns may differ from individual to
individual. A number of studies indicate that a baby’s temperament—how
she responds to stimulation and regulates her emotions—is related to
For instance, studies have shown that babies with “easy”
temperaments—for instance, those who are more adaptable, more
approachable, less distractible, or who generally are in good moods—go
to sleep earlier and sleep more overall than do babies with “difficult”
temperaments (Weissbluth and Liu 1983; Van Tassel 1985; Scher et al
1992; Sadeh et al 1994; Scher et al 1998).
Another study also found that babies rated as more active during
the day had more frequent awakenings at night (Scher et al 1998).
Baby sleep patterns and development: How major milestones can change sleep
Baby sleep patterns are affected by several important developmental milestones:
• Circadian rhythms. As a newborn, your baby will not be very
tuned into the natural daily cycle. Newborns sleep at intervals around
the clock. But gradually they will adapt to the rhythms of the 24 hour
day, and do most of their sleeping at night. Some babies may reach this
point by 3 months. At about the same time, these babies begin “sleeping
through the night,” i.e., sleeping for as long as 5 hours at a stretch.
Other babies may take much longer—over 5 months—before they reach this
milestone (Jenni et al 2006). For tips on how to help your new baby
develop her own circadian rhythms, see my article on
newborn sleep patterns.
• Separation anxiety. Around 6 months of age, your baby’s brain starts
to mature in ways that greatly enrich her emotional life (Eliot 1999).
She begins to be aware of her own feelings, and she begins to form a
strong emotional attachment to her primary caregiver (Eliot 1999). This
may explain why many babies that were previously settled at night become
more needy. Once your baby starts forming strong attachments, she is
more likely to feel separation anxiety. She is more likely to anticipate
your departures and protest. And she is more likely to become upset if
she awakens and you’re not there.
• Teething. Surprisingly, scientific studies reveal that teething
rarely disrupts the sleep of most infants (Wake et al 2000). However,
some infants will suffer sleep problems for a few days before and after a
new tooth erupts.
• Mastering new motor skills. When babies are learning to crawl
or walk or accomplish other milestone feats, the excitement may
interfere with sleep. During such periods, babies may be more resistant
to bedtime and/or experience more night wakings.
Other factors affecting baby sleep patterns
Baby sleep patterns may be disturbed by a number of organic problems, including
• Ear infections
• Yeast and urinary tract infections
• Parasitic infections (like pinworms)
• Respiratory infections
• Acid reflux (Kahn et al 1991)
• Cow's milk allergy (Kahn et al 1989)
• Snoring and sleep apnea
These problems require medical treatment. If you suspect your
baby suffers from one of these problems, you should check with your
pediatrician. (For more details, see my article on
medical problems and their effects on baby sleep patterns.)
But sleep researchers (e.g., France and Blampied 1999) say that most
disturbances in baby sleep patterns are caused by environmental or
behavioral factors, such as
• Overly-stimulating bedtime rituals or soothing behaviors
• Unrealistic parental expectations about how much sleep the baby needs
• Napping in the late afternoon or early evening
• Too much activity in the hours immediately preceding bedtime
• Too much exposure to artificial lighting during the night (and/or insufficient light exposure during the day)
• Disruptions in family life, such as the birth of a sibling
For more information about these factors--and how to improve baby sleep patterns--see this article on
infant sleep problems.
References: What scientific studies reveal about baby sleep patterns
For a complete list of the studies and publications cited in this article,
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