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Keywords:

  • actigraphy;
  • development;
  • infant;
  • sleep/wake patterns

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Maturation of sleep/wake patterns is one of the most important physiological developments during the first year of life. In this study, we aimed to compare the use of actigraphy and parental sleep diaries (SD) for recording the development of sleep/wake patterns longitudinally in term infants in their own home environments over the first 12 months of life. Twenty healthy term infants (7F/13M) were studied for 3 days each month in their own homes over the first 12 months of life. Sleep/wake patterns were recorded using both SD and actigraphy (AW) (AW64, Mini Mitter Co. Inc., Sunriver, OR, USA). The development of sleep and wake was analysed over 24 h, during the day (08:00–20:00 hours) and during the night (20:00–08:00 hours). A total of 186 studies had complete data sets for both analysis methods. Overall, there was no difference between methods of measurement for determination of the total percentage of sleep or wake over 24 h, or for the total percentage of sleep or wake during the day. However, at night, AW scored less time asleep (73.3 ± 0.9%) and more time awake (26.7 ± 0.9%) compared with the SD (80.7 ± 1.04% and 19 ± 1.0%, respectively, P < 0.001). Mean percentage sleep during the day decreased from 51% at 1 month to 28% at 12 months with the 1-month values being significantly higher than all other ages, while mean percentage sleep at night was only different between 1 month and 11 and 12 months. In conclusion actigraphy provides a useful tool for assessing the development infant sleep.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Newborn infants spend around 70% of each 24 h asleep and the development of sleep/wake patterns is one of the major physiological changes occurring over the first year of life (Curzi-Dascalova and Challamel, 2000). This maturation coincides with the maturation of the central nervous system and ‘infant sleep can be regarded as a window to the developing brain’ (Kohyama, 1998). Indeed, it has been proposed that any deviations to the normal development of sleep could highlight a problem within the developing central nervous system (Kohyama, 1998). In support of this idea, it has been shown that sleep/wake organization in both term and preterm infants is a predictor of later cognitive development (Beckwith and Parmelle, 1986; Borghese et al., 1995; Gertner et al., 2002; Whitney and Thoman, 1993).

Infant sleep problems are among the most prevalent problems presented to clinicians and child-health professionals with a reported incidence of around 30% (Armstrong et al., 1994). These problems can range from disrupted sleep patterns with frequent night awakenings to sleep deprivation. The long-term consequences of poor sleep patterns are known to be slow growth, behavioural problems, poor school performance, family disruption and even child abuse (Owens and Witmans, 2004). To date, however, there have been relatively few longitudinal studies examining the development of sleep in infants in their own home environment to define normal infant sleep development (Jenni et al., 2004; Louis et al., 1997), with the majority of studies being carried out in the sleep laboratory, cross-sectionally, for overnight periods only, or have only covered the first 6 months of life (Anders et al., 1995; Anders and Keener, 1985a,b; Coons and Guilleminault, 1982; Hoppenbrouwers et al., 1988).

Actigraphy provides a useful tool which has advantages over other methods of sleep/wake assessment in that it provides a non-invasive, continuous assessment, which can be used for prolonged periods of time in the home environment. The actigraph continuously records the occurrence of limb movements and then sums the number and intensity of movements for a given epoch length, usually 1 min. Through the use of a specially developed algorithm, the motility levels can be computer scored into states of sleep or wake (Sadeh et al., 1995b; Thoman and Acebo, 1995). Previous studies have reported agreement rates between behaviourally scored sleep and awake and actigraphy of between 54% and 87% in infants aged newborn, 3 and 6 months (Sadeh et al., 1995a) and between 72% and 95% in infants 1, 3 and 6 months of age (Gnidovec et al., 2002). Recently, we validated the use of actigraphy against the gold standard of sleep/wake recording, polysomnography in infants up to 6 months of age, and found agreement rates of 89–94% with the predictive value for determining sleep (PVS) being 97% and sensitivity between 91% and 96% (So et al., 2005).

Thus, the aim of this study was to compare the use of actigraphy and parental sleep diaries (SD) for recording the development of sleep/wake patterns longitudinally in term infants in their own home environments over the first 12 months of life.

Methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Ethical approval for this project was granted by the Southern Health and Monash University Human Research Ethics Committees. Subjects were recruited either via an email invitation sent to all Monash University and Monash Medical Centre staff or from the maternity wards at Monash Medical Centre and Jessie McPherson Private Hospital, Melbourne. Infants were included in the study only if they were born at term (between 38 and 42 weeks gestational age) with normal birth weights and had Apgar scores of ≥8 and both 1 and 5 min. Written informed consent was obtained from parents prior to commencement of the study. Participation in the study was entirely voluntary and no monetary incentive was provided.

Subjects

Initially 26 infants were recruited for this study; however, five infants withdrew after either the first, or second study, and one infant who was later diagnosed with a heart condition which may have affected sleep was excluded from analysis. The analysis group consisted of 20 healthy term infants (13M/7F), born at 40.1 ± 0.3 weeks (mean ± SEM) with birth weights between 2950 and 4752 g (mean 3810 ± 118 g). The median Apgar score for the group was 9 at both 1 and 5 min (range 8–9 at 1 min and 9–10 at 5 min). Ten of the infants were first born and 10 were later born (four were second born, four were third born, one was fifth and one sixth born). All infants were breast fed at the commencement of the study, and only one mother reported smoking one to three cigarettes per day. Maternal age ranged between 25 and 40 years (mean 33) and paternal age ranged between 25 and 40 years (mean 34). All parents had completed secondary education and 17 mothers and 14 fathers had completed tertiary education.

Study protocol

Studies were performed in the infant's own home over three consecutive days (72 h) each month across the first 12 months of life. The studies combined the use of both parental sleep dairies and actigraphy (Actiwatch AW64, Mini Mitter Company Inc, Sunriver, OR, USA). Although designed originally for use in adults, we have recently validated the use of this device in infants under 1 year of age (So et al., 2005). The actiwatch (AW) was held securely in place in a specially designed sleeve bandage, which was comfortable for the infant to wear and was placed around the infant's calf, approximately at the midpoint between the knee and the ankle. The AW was only removed for bathing and the event marker was used to indicate this. Studies commenced at around 10:00 hours on the first day of recording and ended at 10:00 hours on the fourth day.

Parent(s) completed a sleep questionnaire which provided detailed information regarding the infant sleep environment, any illness the infant may have had during the study and any medications taken, the method of feeding, and other information, such as any disruptions to normal sleeping patterns. In addition, a SD (divided into 15-min epochs) was maintained for the duration of the study, on which was noted the time the infant was put down to sleep, and the time the infant awoke, together with the timing of feeds/meals for the 3 days of the study.

Data analysis

For this study, daytime was defined as 08:00–20:00 hours and night-time as 20:00–08:00 hours as previously described in the literature (Gang et al., 1993; Rigda et al., 2000). SD were analysed manually and actigraphy data using the Actiwatch software (Actiware®-Sleep V3.3) on the auto setting. Actigraphic data recorded in 1-min epochs were grouped into 15-min epochs to match SD data for the total study duration. Total percentage of sleep and awake over each 24 h, total percentage of sleep and awake during the daytime and night-time were calculated for both methods of recording sleep/wake. Total number of awakenings and length of longest awakening and longest sleep during the night and total number of sleep bouts during the day, together with the number of feeds were recorded from SD only. AW data also included external movements, such as rocking the infant or travelling in a car. Data for each variable were then averaged over the 3 days of the study for each infant. Studies were scheduled to begin and end at 10:00 hours. Data for that day were excluded if the study began after 11:00 hours on the first day, finished before 08:00 hours on the fourth day, or if the SD was incomplete.

To compare the AW with the SD, the two recording methods were matched for each study so that they both had the same start and finish times and the same number of days and nights excluded (if necessary). The two methods of sleep/wake determination were compared with paired Student's t-test and across age with Kruskal–Wallis one way anova. Differences between gender and parity were examined using a non-paired Student's t-test. Results were considered statistically significant at the level of P < 0.05. All values are reported as mean ± SEM.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

A total of 215 studies of a possible 240 were completed successfully and 186 studies with complete data for both AW and SD were analysed. Individual infants had complete data sets for both AW and SD for between seven and 12 studies and 13 and 18 infants had data at each age studied.

Comparison of methods of sleep/wake determination

Comparisons of data recorded by AW and SD are presented in Fig. 1. Overall, there was no difference between methods of measurement for determination of the total percentage of sleep or wake over 24 h, or for the total percentage of sleep or wake during the day. However, at night, AW scored less time asleep (73.3 ± 0.9%) and more time awake (26.7 ± 0.9%) compared with SD (80.7 ± 1.04% and 19 ± 1.0%, respectively, P < 0.001). The percentage of sleep and wake recorded over the 24 h at each age studied was different between AW and SD at 1 month when the AW overestimated sleep (P < 0.01), 2 months (P < 0.05), 5 months (P < 0.05), 9 months (P < 0.05) and 11 months (P < 0.01) when the AW underestimated sleep (Fig. 2). The percentage of sleep and wake during the daytime was only different between methods at 1 month of age when the AW overestimated sleep (P < 0.05, Fig. 3). By contrast, at night-time, there was a difference between methods at 1, 2, 3, 4, 5, 7, 9, 10, 11 and 12 months with the SD overestimated sleep at all ages with the exception of 1 month (Fig. 4).

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Figure 1.  Overall percentage time (min) spent asleep during the day (08:00–20:00 hours), at night (20:00–08:00 hours), over 24 h, time spent awake during the day, awake at night and over 24 h as recorded by sleep diary (black bars) and actiwatch (white bars).

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Figure 2.  Mean percentage total time spent asleep and awake during the 24 h during the first 12 months of life. *P < 0.05 actiwatch versus sleep diary. **P < 0.01 (actiwatch versus sleep diary); #P < 0.05 (1 month versus other ages).

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image

Figure 3.  Mean percentage total time spent asleep and awake during the day (08:00–20:00 hours) during the first 12 months of life. *P < 0.05 (actiwatch versus sleep diary); #P < 0.05 (1 month versus other ages).

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image

Figure 4.  Mean percentage total time spent asleep and awake during the night (20:00–08:00 hours) during the first 12 months of life. *P < 0.05 (actiwatch versus sleep diary); **P < 0.01 (actiwatch versus sleep diary); ***P < 0.001 (actiwatch versus sleep diary); #P < 0.05 (1 month versus other ages).

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Longitudinal development of sleep/wake patterns

Sleep diary data showed no difference across the 12 months in total percentage sleep over 24 h; however, AW showed more total percentage sleep at 1 month than at any of the other ages with the exception of 2, 6 and 12 months (Fig. 2). When data were analysed for daytime sleep infants spent equal amounts of time asleep and awake at 1 month of age. Daytime sleep then decreased across the 12 months being significantly less than at 1 month at all other ages except 2 months for AW and at 5 months and 7–12 months for the SD (Fig. 3). Conversely, the time spent awake during the day increased rapidly over the first 4 months to occupy about 70% of the day and this remained consistent until 12 months of age (Fig. 3). When data were analysed for night-time sleep, there was no difference across the ages for AW data; however, from the SD records infants had more sleep at 11 and 12 months than at 1 month (Fig. 4).

Changes in the number of daytime and night-time feeds

The average number of feeds recorded from the SD during the daytime and night-time are presented in Fig. 5. The number of feeds during the day remained constant across the first 12 months of life averaging around five. The average number of night-time feeds consistently decreased from between two and three at 1 month to less than one at 12 months.

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Figure 5.  Average number of daytime and night-time feeds recorded from the sleep diary during the first 12 months of life.

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Changes in the number of naps during the day and the number of awakenings at night

The changes in the number of naps during the day and the number of awakenings during the night over the first 12 months of life recorded from SD are shown in Fig. 6. Both the number of naps and night-time awakenings decreased with increasing postnatal age. At 1 month of age there was an average of 3.5 naps during the day and 2.5 awakenings at night, which decreased to 2 and <1, respectively, by 12 months. The length of the longest sleep period and longest awakening at night are presented in Fig. 7. There was a significant increase in the longest sleep period from 5 months of age with values being significantly different from that recorded at 1 month. By contrast, the length of the longest night awakening decreased with age with values being significantly shorter at 7 months and 9–12 months compared with 1 month of age. In addition, night awakenings were also shorter at 12 months compared with 2 and 3 months of age.

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Figure 6.  Average number of sleeps during the day and awakenings at night recorded from the sleep diary during the first 12 months of life.

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Figure 7.  Average length of longest night sleep and night awakening recorded from the sleep diary during the first 12 months of life. *P < 0.05 (1 month versus other ages); #P < 0.05 (2 months versus other ages); §P < 0.05 (3 months versus other ages).

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Differences in sleep/wake patterns between male and female infants

Data for sleep/wake patterns were examined for differences in developmental patterns between male (n = 13) and female (n = 7) infants. There were no differences in the percentage time spent asleep or awake over 24 h at any age, or the time spent asleep or awake at night. However, male infants spent less time asleep during the day than did female infants at 1 month for both SD (44 ± 2% compared with 52 ± 3%, P < 0.05) and AW (50 ± 2% compared with 66 ± 8%, P < 0.05). There was also a difference at 2 months where again males spent less time asleep than females as recorded by the AW (38 ± 3% compared with 49 ± 3%, P < 0.05), this just failed to reach significance for the SD (32 ± 2% compared with 39 ± 2%, P = 0.06). There was no difference in the length of the longest night sleep period between the sexes; however, at 3 months of age female infants had longer night awakenings (120 ± 18 min) compared with male infants (73 ± 12 min, P < 0.05).

Differences in sleep wake patterns related to birth order

The comparison of the development of sleep between first born (n = 10) and later born (n = 10) infants showed no statistical significance for either SD or AW for total sleep over 24 h, daytime or night-time sleep at any age with the exception of the amount of sleep at night at 7 months for the SD when first born infants sleep longer (88 ± 2%) compared with later born infants (81 ± 2%, P < 0.02), the AW data did not record a difference.

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

This was the first study to follow healthy term infants longitudinally over the first year of life using a combination of actigraphy and parental SD to investigate normal patterns of sleep development. We found a good correlation between the two methods of measurement for total sleep and wake over 24 h and for daytime sleep and wake; however, the AW overestimated night-time waking and underestimated night-time sleep compared with the SD. Importantly, both methods found that daytime sleep decreased with postnatal age, while the percentage of total wake time and daytime wake increased. Conversely, we found that during the night-time period the percentage of total sleep and length of longest sleep period increased and the number and duration of night-time awakenings decreased as the infant matured. Furthermore, our study found no significant differences in sleep/wake patterns found between boys and girls or between first born and later born infants.

Comparison of methods of sleep/wake determination

This study found that overall parental SD and actigraphy recorded similar amounts of sleep and wake over the first 12 months of life when averaged over 24 h or over the daytime period. However, sleep and wake at night were overscored and underscored, respectively, by the parental SD. When the two methods were compared at each age studied there were significant differences in the amount of sleep and wake over 24 h at 1, 2, 5, 9 and 11 months of age. The difference was most marked at 1 month of age when the AW recorded more sleep and less wake than the SD by an average of 9.4% or around 2 h. The differences at the later ages, although statistically significant were smaller ranging from 3.8% to 4.4% or around 1 h and in contrast to the findings at 1 month of age, at these ages the SD recorded more sleep and less wake than the AW. For recording sleep and wake during the day, the two methods of measurement were only different at 1 month of age. By contrast, when recording sleep and wake at night, the two methods only recorded similar results at 6 and 8 months of age. As with the findings of differences between recording methods during the day, at 1 month the AW recorded more sleep and less awake than the SD, whereas the converse was found at all later ages with the SD recording more sleep and less wake than actigraphy. The difference found at 1 month of age when the SD recorded less sleep compared with the AW, which was in contrast to the findings at the other ages may have been due to the activity threshold setting of the AW which was auto for all studies. Previously, we have found that the low-activity threshold setting was more sensitive in younger infants (So et al., 2005). In addition, other studies have reported that actigraphy is less reliable in younger infants (Gnidovec et al., 2002; Sadeh et al., 1995a).

This difference between recordings made using actigraphy and SD has also been reported by Sadeh (1996), who found SD also overestimated sleep, however, by a smaller amount of an average of 14 min and under estimated night awakenings. Sadeh also reported that there was a tendency for the accuracy of some measures, such as sleep duration, sleep percentage and night awakenings to decrease over the 7 days of recording (Sadeh, 1994, 1996). Sadeh suggested that the differences could have been due to the parents being exhausted by the having to keep a diary over 7 days (Sadeh, 1994, 1996). Our study was only carried out over 3 days and we averaged the data over this time period and did not examine the differences between the first and last recording days as the aim of the study was to obtain a typical sleep pattern recording. An alternative explanation for the discrepancies found, is that the infants awoke but did not cry and were able to get themselves back to sleep without altering the parents to their awakening. Our finding that there was no difference between methods of recording during the daytime would support this idea.

Longitudinal development of sleep/wake patterns

24-h period

Our studies demonstrated that total sleep time over a 24-h period decreased as the infant aged, beginning at around 60% at 1 month of age and then flattening out at 3 months of age where it remained relatively constant at around 50–55% up until 12 months of age. These findings are in accordance with earlier studies examining the development of sleep–wake patterns in normal infants and the development of sleep described in textbooks on infant sleep which have concurrently found and described that the proportion of total sleep time over a 24-h period decreases with age from approximately 60–70% at 1 month of age (Coons, 1987; Coons and Guilleminault, 1982) to about 50–55% (Anders et al., 1995; Anders and Keener, 1985; Buckley et al., 2002; Coons and Guilleminault, 1982; Louis et al., 1997; Parmelee et al., 1964; Rigda et al., 2000; Sheldon et al., 1992). These findings are consistent with a longitudinal home study using 24-h polygraphic recording of infants between 3 and 24 months of age which found that total sleep time decreased most rapidly between 3 and 6 months (Louis et al., 1997).

Daytime and night-time sleep–wake patterns

Our studies showed that at 1 month of age, the proportion of time spent asleep during the day is approximately equal to the time spent awake. Over the first 4 months, the amount of time spent awake during the day increased, while the amount of time spent asleep decreased. From around 4 months of age, the time spent asleep and awake during the day remained relatively consistent. A study using SD, although showing similar trends in the development of sleep–wake, had overall higher proportions of sleep during the day starting at approximately 65% at 3 months of age (Parmelee et al., 1964). This difference may be due to the fact that the mothers were asked only to record data after each feed or at least twice daily, thus maybe causing the majority of mothers to be very approximate with the times and also having to rely on their memories.

From our analysis of the development of the proportion of time spent asleep and awake during the night, our SD data showed that the proportion of sleep increased with age and wakefulness conversely decreased. In addition, the length of night-time sleep epochs increased, while time spent awake decreased. This trend is consistent with previous studies (Louis et al., 1997; Parmelee et al., 1964). Although the trends are similar in the study performed by Louis et al. (1997) using polygraphic recordings, they reported higher overall proportions of time spent asleep at each month than in our study.

Changes in the number of naps during the day and the number of awakenings at night

Our studies found that infants initially take approximately 3.5 naps during the day at 1 month, which consolidates to around two naps by 12 months. Our results regarding daytime naps are consistent with the current knowledge as described in Anders et al. (1995). In addition, night wakings tended to decrease in the number as the infant matured, from around 2.5 times at 1 month to <1 times at 12 months. These numbers are similar to those reported for 1- and 3-month-old breast-fed infants (Ball, 2003). Importantly, at 12 months of age, not all infants are sleeping throughout the night. These findings agree with studies investigating night wakings in infants as they found that it was common for infants to not sleep throughout the night even at 12 months of age (Anders, 1979; Anders et al., 1992; Armstrong et al., 1994).

Differences in sleep/wake patterns between male and female infants

Our studies found that there were no significant differences between male and female infants in the proportion of time spent asleep and awake at each age. These findings are supported by those of pervious studies which also showed no difference in total sleep time in a much larger group of infants at 6, 13, 26 and 52 weeks postnatal age (Bamford et al., 1990). Our findings that male infants spent more time awake during the day at 1 and 2 months of age than female infants has not been reported previously. These findings may have been due to the small sample size of female infants (n = 7) in our study.

Differences in sleep/wake patterns related to birth order

We had speculated that an infant's sleep pattern may be altered as a result of parental experience; however, our studies found that there were no differences in the development of sleep/wake patterns between first born and later born infants.

Conclusions

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Our study found that in the home setting, actigraphy gave similar results for the total sleep and wake percentages when compared with the SD during the day. However, during the night, it was found that the SD underestimated night awakening compared with the AW. In addition, we also found that the 24 h, daytime and night-time trends for the longitudinal development of sleep/wake patterns in infants were comparable with that previously reported. Thus, actigraphy is a viable alternative to SD in studying sleep and wake patterns in the home environment.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

The authors thank the parents and infants (Liam, Alysha, Daragh, Chloe, Mitchell, Liam, Luke, Christopher, Kara, Daniel, Nicholas, Alec, Thomas, Felicity, Emma, James, Alyssa, Xavier, Liam, Teylahne and Adam) who participated in this study.

This project was supported by grants from the Bonnie Babes Foundation, Ramaciotti Foundations for Biomedical Research, Karitane and SIDassist.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References
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