The Role of Intrinsic and Extrinsic Factors in Infant Night Waking.

Parents of young infants are faced with a number of adjustments and challenges. In particular, during the first few weeks or months following birth, infants require feeding at regular intervals throughout the day and night. Infants signal their need to be fed by crying, and thus the nighttime sleep of parents is frequently disrupted by the cry signal and the need to awaken to feed the infant, change the infant's diaper, and soothe the infant back to sleep. Most parents know to expect these interruptions to their sleep during early infancy, and many mothers and some fathers are able to devote full time to the many demands of caring for a young infant by foregoing employment or taking maternity or paternity leave from their jobs. By 3-4 months, however, most infants no longer physiologically require night feedings, and most infants have adapted to a daily rhythm in which they sleep more at night than during the day. Although essentially all infants continue to awaken at night at 3 months, about half of them are able to return to sleep without signaling and without parental intervention (Karraker & Cottrell, 2000). The other half signal to their parents when they awaken, and often require feeding, rocking, and other parental assistance to return to sleep. These signaled night awakenings continue throughout the first year and beyond for a significant proportion of infants, and some infants who begin to "sleep through the night" (meaning that they do not signal to their parents following an awakening) at some point in early infancy return to a pattern of signaled night waking around 9 months. These signaled night waking behaviors (henceforth referred to simply as "night waking") beyond the first few months of infancy are the focus of the present discussion. They are of concern to parents and practitioners primarily because of their impact on parents. Parents whose sleep is frequently shortened and fragmented experience substantial sleep deprivation, which can cause daytime fatigue, irritability, motor and cognitive deficits, impaired decision making, and lack of motivation (Dement, 1999; Pilcher & Huffcutt, 1996). It has been estimated that parents of infants lose an average of 2 hours of sleep per night from birth to 5 months, and 1 hour of sleep per night from 6 to 24 months (Dement, 1999). Sadeh and Anders (1993) also report that infant sleep difficulties are the most common concern parents report to pediatricians at well-baby visits. The present paper addresses what is known about infants' night waking, with a focus on the role of environmental causes and correlates of individual differences in this behavior. To provide context, the discussion begins with a review of the normative developmental course of infant night waking, followed by a description of the effects of sleep deprivation on adults. Then, factors associated with individual differences in the frequency of night waking are described. Both intrinsic factors (characteristics of infants) and extrinsic factors (parent behaviors, family environment, etc.) are addressed. Then, the types of interventions commonly used to reduce infant night waking are summarized. Finally, a behavioral and developmental model of the causes and effects of infant night waking is described and illustrated. Normative Developmental Changes in Night Waking During Infancy Information about infant sleep behavior is based primarily on maternal reports, video recordings, and actigraph recordings. An actigraph is a wristwatch-like device that is typically attached to the infant's leg and that records movements for later analysis. Hayes (2002) discussed the relative value of these different methods. Although video and actigraph recordings are more objective and detailed than maternal reports, they can be costly, intrusive, and difficult to use. Further, the sole use of actigraph recordings makes it difficult to discriminate signaled and unsignaled night waking events. …