Maintaining a suitable sleep environment is critical to an infant’s sleep/wake schedule
By Theresa Shumard
Richard Ferber, MD, director of pediatric sleep disorders at Children’s Hospital, Boston, says that to understand sleep patterns and certain problems associated with childhood sleep problems, it is important to first conceive underlying circadian rhythms. According to Ferber, circadian rhythms are biological cycles that repeat about every 24 hours and include periods of wake and sleep, activity and rest, hunger and eating, and oscillations in hormone release and body temperature. Cycles must be in accord to lend a sense of well-being during the day.
The circadian rhythms of human infants—especially the alteration of sleep and wakefulness-—differ from the circadian rhythms of adults. Adults generally fall asleep at night and remain asleep through the early morning hours. However, an infant falls asleep and awakens in 3- to 4-hour cycles throughout the night and early morning hours, a fact that parents often dread since an awakened baby may frequently interrupt their own sleep. Consequently, parents and pediatricians seek the key to synchronizing infant sleep schedules with those of their adult caretakers.
“This often proves initially to be a difficult task considering the dramatic differences in sleep patterns and biological rhythms between adults and infants,” says Michael J. Harnish, PhD, clinical director of the Oklahoma Center for Children’s Sleep Disorders, Oklahoma City.
In infants, stages of sleep are categorized according to behavior as active sleep or quiet sleep, instead of the familiar system used in adults that categorizes sleep as either non-rapid eye movement (NREM) or rapid eye movement (REM). NREM sleep is further divided into four discrete stages (labeled stages 1 through 4), based on electrophysiological markers. At birth, an infant’s normal sleep stage percentages of active and quiet sleep are equal. By the first 2 weeks of life, these percentages gradually begin to change, and the baby spends increased amounts of time in quiet sleep. By the time the child reaches 6 months of age, quiet sleep makes up about 70% of their sleep, and active sleep makes up 30%.1
Since many of the well-known electrophysiological markers seen in adults are absent in infants, scientists use a simplified sleep staging system to describe sleep in infants. According to Harnish, behavioral observation is often the best measure of sleep during the first few months of life. Sleep is entered through active sleep during the first 6-7 months.
Active sleep is usually achieved in about 90 minutes in adults; however, active sleep that occurs at sleep onset in newborns will usually begin to shift to quiet sleep at sleep onset by the third month of the baby’s life. Longer, more consolidated periods of wakefulness usually begin to appear by 6 weeks of age. After 9 weeks of age, wakefulness is typically distributed during the late afternoon and early evening.2
“Newborns typically sleep about 17 hours per day during the first weeks of life,” Harnish says. “Although they rarely sleep more than 4 hours at a time, some may sleep through the night by 8 weeks old. By the third month, infants normally sleep 14 to 15 hours per day. While the typical child will begin to demonstrate a diurnal pattern during these first few months, parents can help the infant along by maintaining regular feeding patterns and establishing a bedtime ritual early in the child’s life.”
Infants have varied temperaments and families have varied lifestyles. Developing a nighttime schedule that fits these needs is a challenge for many families. It is helpful to be open to different nighttime approaches, but parents should be careful about using someone else’s method to get their baby to sleep. Consideration of any advice should be approached with sensitivity to the infant’s temperament and individual family situations.
Facts about infant sleep
Why babies wake up at night
Helping baby sleep
Adapted from Passmark L. Infant Sleep, Early Childhood Development Tips. Oklahoma City: Parent Education Program, Oklahoma State Department of Health; 2000.
According to Harnish, the timing of naps affects the type of sleep that occurs during infant napping. He warns that parents whose children have developed poor nighttime sleeping habits should not deter daytime naps because infants need them. However, parents also should not provide the child with too many opportunities to nap during the day or the consolidation of the nighttime sleep period can be undermined. Infants up to 4 months of age usually take two to three naps per day. By 6 months of age, most infants are down to two naps per day (midmorning and midafternoon), and typically abandon the mid-morning nap by the age of 2 years. A child may continue to nap once per day, usually in the mid-afternoon, until the age of 4 or 5.
FEEDINGS AND INFANT SLEEP
When an infant is ready for solid foods, the child’s sleeping habits may change. Solids may also initially cause some sleep disturbance as an infant’s developing digestive system becomes acclimated to the new foods. Infants may also require more time to fall asleep (approximately 25 minutes). However, as the child grows, the time needed before sleep is achieved decreases, while the duration of a sleep episode increases. By 6 months of age, most infants are sleeping for at least 5 hours in a row.3
Daily schedules and environmental cues play an important role in the infant learning that daytime is for wake and night for sleep, according to Harnish. If a regular schedule is not maintained, the child’s sleep cycle may become erratic, a phenomenon most parents find very frustrating. Often the parents are the root of the problem because they fail to set adequate limits or they maintain an erratic activity schedule around the child.
If an infant’s daily schedule is too irregular, then sleep at night may be fragmented. Keeping a routine for the family during the first few months of the newest member’s life can be pleasant for all. As the infant grows older, the child learns through social cues from the family about appropriate sleeping patterns. The baby eventually recognizes that day is for awake and night is for sleep. These cues derive from daily family activities, the natural light of daytime, and the natural darkness of night.
A common scenario is where the parents complain that the child wakes up too early. According to Harnish, when the child’s sleep schedule is examined, it is often discovered that the child’s bedtime is set too early, thereby naturally advancing the morning wake time. In other extreme cases, a child’s sleep/wake schedule may become completely irregular or may begin to run exactly opposite to a normal diurnal pattern.
Maintaining a suitable sleep environment is critical to children following a normal sleeping routine. During the day, when children are awake, their room should not be kept dark or too quiet. Normal environmental noise and lighting should be used. At night overstimulation through excessive talking to the infant or exposing him to bright light levels might similarly send the wrong message. Harnish says that parents who find themselves with night-owl infants should wake them up at a normal time, keep the home bright during the day, and stimulate the children to be awake more by providing more play time. He advises that these infants should be awakened from naps for feedings if necessary in order to establish and maintain a more appropriate sleep/wake schedule.
At the time we awake, body temperature normally starts rising toward a peak, and when we fall asleep, our body temperature normally falls to a daily minimum. Secreted by the adrenal gland, cortisol hormone levels also diminish during the night and rise when we approach the time of waking. If body temperatures do not follow this pattern, we have difficulty falling asleep and awakening.4 A recent study revealed that changes in ambient temperatures associated with mild increases in body temperature significantly modified cardiorespiratory parameters and autonomic controls in healthy infants. The changes associated with increases in temperature were mainly seen during REM sleep.5
CAREGIVER SLEEP DEPRIVATION
Understanding the natural physiological maturation of infant circadian rhythms is not usually weighing heavily on new parents’ minds. Most are interested in remedying their own sleep deprivation caused by caring for their awake infants. For these sleep-deprived parents, strategies for dealing with their baby’s shorter sleep/wake cycles may seem more notable than scientific observations about circadian rhythms.
Eventually the sleep-wake schedule will consolidate as the circadian rhythm of the infant matures. Parents and caregivers should be advised that compromises should be considered with a new infant. In the meantime, rotating night duty with a spouse or another family member can give a bit of relief to sleepy parents.
Theresa Shumard is editor in chief of The A2Zzz, the newsmagazine for the Association of Polysomnographic Technologists; founder of REMgazer Sleep Communications; and manager of operations for the Lynn Health Science Institute Sleep Disorders and Research Laboratories in Oklahoma City.
1. Ferber R, Kryger M. Principles and Practice of Sleep Medicine in the Child. Philadelphia: WB Saunders; 1995.
2. Sheldon SH. Evaluating Sleep in Infants and Children. Philadelphia: Lippincott; 1996.
3. Passmark L. Infant Sleep, Early Childhood Development Tips. Oklahoma City: Parent Education Program, Oklahoma State Department of Health; 2000.
4. Ferber R. Solve Your Child’s Sleep Problems. New York: Simon & Schuster, 1986.
5. Franco P, Szliwowski H, Dromoix M, Kahn A. Influence of ambient temperature on sleep characteristics and autonomic nervous control in healthy infants. Sleep. 2000;23:401-7.