Nighttime sleep-wake patterns and self-soothing from birth to one year of age: a longitudinal intervention study.

For infants who sleep independently, the ability to self-soothe when falling asleep at the beginning of the night and following nighttime awakenings appears to be a key ingredient for the development of healthy sleep-wake patterns. Although a number of studies have described the development of sleep-wake patterns during infancy, relatively few have examined factors related to the emergence of self-soothing behavior. Theoretically, self-soothing refers to an infant’s ability to regulate states of arousal; for example, calming from crying to quiet wakefulness without parental assistance. In this study, self-soothing refers to an infant’s ability to settle to sleep at the beginning of the night and to put herself back to sleep upon awakening during the night. The purpose of the current study was to objectively monitor infant sleep-wake patterns and other variables thought to relate to the development of self-soothing across the first year of life. The development of sleep-wake patterns follows a somewhat prescribed path during infancy. First, the 24-hour distribution of sleep changes across the first year. Newborns tend to sleep for 16–17 hours in 3–4 hour increments dispersed throughout the 24-hour day (Parmelee, Shulz, & Disbrow, 1961). By 1 year of age, the bulk of sleep shifts to the nighttime hours and sleep periods lengthen (consolidate), but the total amount of sleep per 24 hours decreases relatively little (Anders & Keener, 1985; Kleitman & Engelmann, 1953). Second, the proportions of sleep states change with age, such that rapid eye movement (REM) or active sleep decreases and non-rapid eye movement (NREM) or quiet sleep increases over the first year (Anders & Keener, 1985; Fagioli & Salzarulo, 1982). Although these basic patterns have been confirmed by numerous studies over the past 40 years, few large-scale longitudinal investigations have examined factors associated with the development of nighttime self-soothing. The few investigations that have examined falling asleep and self-soothing after nighttime awakenings during the first year of life have shown that this ability develops in some infants, but not others, by the end of the first year (Anders, Halpern, & Hua, 1992; Keener, Zeanah, & Anders, 1988; Goodlin-Jones, Burnham, Gaylor, & Anders, 2001; Goodlin-Jones, Eiben, & Anders, 1997). During the first months of life, infants most often fall asleep during or immediately after a feeding both at the beginning and during the middle of the night; self-soothing is observed only occasionally. By 4 to 6 months of age, however, self-soothing behaviors at sleep onset and following nighttime awakenings begin to appear in some infants and tend to increase in frequency to the first birthday (Goodlin-Jones et al., 2001). Infants who self-soothe are generally considered by parents to be better sleepers than infants who consistently need assistance to make the wake-sleep transition. Infant sleep disturbances are often brought to the attention of pediatricians during well-child visits due to the sleep disruption imposed on families (Lozoff, Wolf, & Davis, 1985). Indeed, France and Blampied (1999) define a sleep-disturbed infant as ‘one who is unable to settle back to sleep without the parents being aware of the awakening’. More precisely, awakenings are most disturbing to parents when the child cannot return to sleep on her own and requires parental intervention. For the purposes of the current investigation, these infants are considered ‘non-self-soothers’. Clearly, infants who do not develop the ability to self-soothe can create turmoil in some families. A simple linear model that describes the emergence of self-soothing is not sufficient. A transactional model embraces the complexities of interacting systems or domains across a developmental time span (Sameroff & Fiese, 2000). A transactional perspective to self-soothing might include infant characteristics, parental characteristics, and interactions between infants and parents. Figure 1 displays a tentative model of potential domains associated with self-soothing (Anders, 1994; Goodlin-Jones, Burnham, & Anders, 2000). Variables in the four domains are thought to relate to each other and, ultimately, to whether the child is or is not able to self-soothe to sleep from the waking state. The model reflects the notion that self-regulation of wake to sleep transitions results from a dynamic, interactive process between the infant and a number of proximal and distal influences, mediated mostly through interactions with caregivers. This model is a work in progress. Thus far, partial support for the transactional model comes from small-scale and/or cross-sectional investigations (e.g., Goodlin-Jones et al., 2001). There have been no longitudinal studies specifically designed to investigate the hypothesized links. Figure 1 A transactional model for the development of self-soothing behaviors related to wake-to-sleep state transitions. The model, derived from empirical and clinical experience, provides a framework to guide investigation. More research is required to assess ... Within the infant domain, the variable receiving most research attention in relation to infant sleep has been temperament. Infant temperament has been consistently, albeit moderately, related to the quality of nighttime sleep (Halpern, Anders, Garcia Coll, & Hua, 1994; Minde, Popiel, Leos, Falkner et al., 1993; Scher, Tirosh, & Lavie, 1998; Van Tassel, 1985). An association between temperament and middle-of-the-night self-soothing also has been reported (Keener et al., 1988). Fathers were found to rate non-self-soothing infants as more temperamentally difficult than self-soothing infants; however, a similar relationship did not hold for mothers’ ratings of temperament. Minde and colleagues (1993) reported an association between difficult temperament and problem sleep. In their study, problem sleepers were unable to return to sleep without a parental intervention (i.e., they were non-self-soothers). Parental factors also have been associated with infant sleep disruption. Seifer and colleagues (Seifer, Sameroff, Dickstein, Hayden, & Schiller, 1996) reported an association between both higher levels of maternal mental illness and lower levels of overall family functioning and bedtime problems in toddlers. Benoit, Zeanah, Boucher, and Minde (1992) found that all of the sleep-disturbed toddlers in their sample had mothers with insecure attachment styles. Another study, however, failed to find a relation between maternal psychological well-being and infants’ tendency to self-soothe during the night. This null finding may have been due to the non-clinical range of maternal depression scores reported in this study (Goodlin-Jones et al., 2001). Associations between the sleep context and sleep-wake domains and self-soothing have been illustrated most clearly to date. Infants who are placed into their cribs awake at the beginning of the night and who use a sleep aid are more likely to self-soothe than their counterparts (Anders et al., 1992; Goodlin-Jones et al., 1997). In addition, self-soothing infants have longer continuous sleep periods and longer total sleep times at night (Anders et al., 1992; Goodlin-Jones et al., 2001). There is clearly some evidence in support of the relationships between each of the model domains and nighttime self-soothing. A more detailed review of these associations has been published recently (France & Blampied, 1999). The current study had three goals. As the first relatively large-scale longitudinal study to objectively investigate infant sleep, the first goal was to replicate previous work on the basic patterns of sleep-wake development across the first year of life. The second goal was to test a double blind, random assignment intervention trial to enhance self-soothing at night. The third goal was to identify potential factors leading to the development of self-soothing at 12 months of age.