Important Infant Sleep Facts

In order to better understand the how-to’s of getting you and your baby to enjoy going to sleep and staying asleep, here are some important principles of infant sleep that every new parent needs to understand.

1. How You Sleep.

After dressing for bed, most adults help themselves relax for sleep by performing various bedtime rituals. For example, reading, listening to music or watching TV. As you drift into sleep, your higher brain centers begin to rest. Therefore enabling you to enter the stage of deep sleep called “non-REM” (non-rapid-eye movement — NREM), or deep sleep. Your mind and body are quietest during this stage of sleep. Your body is still, your breathing is shallow and regular and your muscles are loose. After about an hour and a half in this sleep stage, your brain begins to “wake up” and start working. This brings you out of your deep sleep and into a light sleep, called rapid eye movement or “REM” sleep.

During “REM” your eyes actually move under your eyelids as your brain exercises. You dream and stir, turn over, and may even adjust the covers without fully awakening. In this sleep stage, you may fully awaken to go to the bathroom, then return to bed and fall back into a deep sleep. These alternating cycles of light and deep sleep continue every couple hours throughout the night. A typical adult may spend an average of six hours in quiet sleep and two hours in active sleep. Thus, you do not sleep deeply all night, even though you may feel as though you do.

2. How Your Infant Sleeps.

You’re rocking, walking, or nursing your baby and her eyelids droop as she begins to nod off in your arms. Her eyes close completely, but her eyelids continue to flutter and her breathing is still irregular. Her hands and limbs are flexed, she may startle, twitch, and show fleeting smiles, called “sleep grins”. She may even continue a flutter-like sucking. Just as you bend over to deposit your “sleeping” baby in her crib so you can creep quietly away, she awakens and cries. That’s because she wasn’t fully asleep. She was still in the state of light sleep when you put her down.

Now try your proven bedtime ritual again, but continue this ritual longer (about twenty more minutes). You will notice that baby’s grimaces and twitches stop; her breathing becomes more regular and shallow, her muscles completely relax. Her fisted hands unfold and her arms and limbs dangle weightlessly. Martha and I call this “limp-limb” sign of deep sleep. Baby is now in a deeper sleep. You put her down and sneak away, breathing a satisfying sigh of relief that your baby is finally resting comfortably.

NIGHTTIME PARENTING LESSON #1: Babies need to be parented to sleep, not just put to sleep. Some babies can be put down while drowsy yet still awake and drift. Others need parental help by being rocked or nursed to sleep. While adults can go directly into the state of a deep sleep, infants do not. In the early months, infants enter sleep through an initial period of light sleep. After twenty minutes or more they gradually enter deep sleep, from which they are not so easily aroused. If you rush your baby to bed while she is in the initial light sleep period, she will usually awaken. Many parents tell me: “My baby has to be fully asleep before I can put her down”. In later months, some babies can enter deep sleep more quickly. Learn to recognize the stages your infant sleeps in. Wait until your baby is in a deep sleep stage before transitioning her from one sleeping place to another.

3. Babies Have Shorter Sleep Cycles Than You Do.

Stand adoringly next to your sleeping baby and watch him sleep. About an hour after he goes to sleep, he begins to squirm, he tosses a bit, his eyelids flutter, his face muscles grimace, he breathes irregularly, and his muscles tighten. He is reentering the phase of light sleep. The time of moving from deep to light sleep is a vulnerable period. Many babies will awaken if any upsetting or uncomfortable stimulus, such as hunger, occurs. If the baby does not awaken, he will drift through this light sleep period over the next ten minutes. Followed by a descend back into a deep sleep.

Adult sleep cycles (going from light to deep sleep, and then back to light sleep) lasts an average of 90 minutes. Infant sleep cycles are shorter, lasting 50 to 60 minutes. Infants experience a vulnerable period for night-waking around every hour or even less. As your baby enters this light sleep, lay a comforting hand on your baby’s back, or sing a soothing lullaby. If baby is in your bed, be there next to him. You can help him get through this light sleep period without waking.

NIGHTTIME PARENTING LESSON #2: Some babies need help getting back to sleep. Some “resettlers” or “self-soothers” can go through this vulnerable period without completely awakening. If they do wake up, they can ease themselves back into a deep sleep. Other babies need a helping hand, voice, or breast to resettle back into a deep sleep. One of the goals of nighttime parenting is to create a sleeping environment that helps baby go through this vulnerable period of night-waking and reenter deep sleep without waking up.

4. Babies Don’t Sleep as Deeply as You Do.

Not only do babies take longer to go to sleep and have more frequent vulnerable periods for night waking; they have twice as much active, or lighter, sleep as adults. At first glance, this hardly seems fair to parents tired from daylong baby care. Yet, if you consider the developmental principle that infants sleep the way they do — or don’t — for a vital reason, it may be easier for you to understand your baby’s nighttime needs and develop a nighttime parenting style that helps rather than harms the natural infant sleep rhythms. Here’s where I’m at odds with modern sleep trainers who advise a variety of gadgets and techniques designed to help baby sleep more deeply through the night — for a price, and perhaps at a risk.

5. Night Waking Has Survival Benefits.

In the first few months, babies’ needs are the highest, but their ability to communicate their needs is the lowest. Suppose a baby slept deeply most of the night. Some basic needs would go unfulfilled. Tiny babies have tiny tummies, and mother’s milk is digested very rapidly. If a baby’s stimulus for hunger could not easily arouse her, this would not be good for baby’s survival. If baby’s nose was stuffed and she could not breathe, or was cold and needed warmth, and her sleep state was so deep that she could not communicate her needs, her survival would be jeopardized.

One thing we have learned during our years in pediatrics is that babies do what they do because they’re designed that way. In the case of infant sleep, research suggests that active sleep protects babies. Suppose your baby sleeps like an adult, meaning predominantly deep sleep. Sounds wonderful! For you, perhaps, but not for baby. Suppose baby had a need for warmth, food, or even unobstructed air, but because he was sleeping so deeply he couldn’t arouse to recognize and act on these needs. Baby’s well being could be threatened. It appears that babies come wired with infant sleep patterns that enable them to awaken in response to circumstances that threaten their well being. We believe, and research supports, that frequent stages of active (REM) sleep serve the best physiologic interest of babies during the early months when their well being is most threatened.

NIGHTTIME PARENTING LESSON #3 Encouraging a baby to sleep too deeply, too soon, may not be in the best survival or developmental interest of the baby. This is why new parents, vulnerable to sleep trainers’ claims of getting their baby to sleep through the night, should not feel pressured to get their baby to sleep too long, too deeply, too soon.

6. Night Waking Has Developmental Benefits.

Sleep researchers believe that infant sleeping patterns is a “smarter” way to sleep than typical adult sleeping. They theorize that light sleep helps the brain development because the brain doesn’t rest during REM sleep. In fact, blood flow to the brain nearly doubles during REM sleep. (This increased blood flow is particularly evident in the area of the brain that automatically controls breathing.) During REM sleep the body increases its manufacture of certain nerve proteins, the building blocks of the brain. Learning is also thought to occur during the active stage of sleep. The brain may use this time to process information acquired while awake, storing what is beneficial to the individual, and discarding what is not.

Some sleep researchers believe that REM sleep acts to auto-stimulate the developing brain, providing beneficial imagery that promotes mental development. During the light sleep stage, the higher centers of the brain keep operating, yet during deep sleep, these higher brain centers shut off and the baby functions on her lower brain centers. It is possible that during this stage of rapid brain growth (babies’ brains grow to nearly seventy percent of adult volume during the first two years) the brain needs to continue functioning during sleep in order to develop. It is interesting to note that premature babies spend even more of their sleep time (approximately 90 percent) in REM sleep, perhaps to accelerate their brain growth.

As you can see, the period of life when humans sleep the most and the brain is developing the most rapidly is also the time when they have the most active sleep. One day as I was explaining the theory that light sleep helps babies’ brains develop, a tired mother of a wakeful infant chuckled and said, “If that’s true, my baby’s going to be very smart.”

7. As They Grow, Babies Achieve Sleep Maturity.

“Okay,” you say, “I understand this developmental design, but when will my baby sleep through the night?” The age at which babies settle – meaning they go to sleep easily and stay asleep varies widely among babies. For some infants, sleep is easily come by, but they don’t stay asleep. Others go to sleep with difficulty but will stay asleep. Other exhausting babies neither want to go to sleep nor stay asleep.

In the first three months, tiny babies seldom sleep for more than four-hour stretches without needing feeding. Tiny babies have tiny tummies. Yet, they usually sleep a total of 14-18 hours a day. From three to six months, most babies begin to settle. They are awake for longer stretches during the day and some may sleep five-hour stretches at night. Between three to six months, expect one or two night wakings. You will also see the period of deep sleep lengthen. The vulnerable periods for night waking decrease and babies are able to enter deep sleep more quickly. This is called sleep maturity.

NIGHTTIME PARENTING LESSON #4: An important fact for you to remember is that your infant’s sleep habits are more a reflection of your baby’s temperament rather than your style of nighttime parenting. And keep in mind that other parents usually exaggerate how long their baby sleeps as if this were a badge of good parenting, which it isn’t. It’s not your fault baby wakes up.

8. Babies Still Wake Up.

When babies mature into these adult-like sleep patterns varies among babies. Yet, even though babies achieve this sleep maturity some time during the last half of the first year, many still wake up. The reason? Painful stimuli, such as colds and teething pain, become more frequent. Major developmental milestones, such as sitting, crawling, and walking, drive babies to “practice” their new developmental skills in their sleep. Then between one and two years of age, when baby begins to sleep through the above-mentioned wake-up stimuli, other causes of night waking occur, such as separation anxiety and nightmares.

Even though you understand why babies are prone to night waking, you realize it’s still important for parents and babies to get a restful night’s sleep. Otherwise, baby, the parents, and their relationship won’t thrive.

For more information on infant sleep, read “The Baby Sleep Book”

Dr. Sears, or Dr. Bill as his “little patients” call him, has been advising busy parents on how to raise healthier families for over 40 years. He received his medical training at Harvard Medical School’s Children’s Hospital in Boston and The Hospital for Sick Children in Toronto, the world’s largest children’s hospital, where he was associate ward chief of the newborn intensive care unit before serving as the chief of pediatrics at Toronto Western Hospital, a teaching hospital of the University of Toronto. He has served as a professor of pediatrics at the University of Toronto, University of South Carolina, University of Southern California School of Medicine, and University of California: Irvine. As a father of 8 children, he coached Little League sports for 20 years, and together with his wife Martha has written more than 40 best-selling books and countless articles on nutrition, parenting, and healthy aging. He serves as a health consultant for magazines, TV, radio and other media, and his AskDrSears.com website is one of the most popular health and parenting sites. Dr. Sears has appeared on over 100 television programs, including 20/20, Good Morning America, Oprah, Today, The View, and Dr. Phil, and was featured on the cover of TIME Magazine in May 2012. He is noted for his science-made-simple-and-fun approach to family health.