Background
Learning to self-regulate is an essential transactional task between child and caregivers in early childhood, with sleep playing a crucial role in this process [
1‐
5]. Early regulatory problems manifest in a triad of symptoms with child behavior problems and severe parental distress and a dysfunctional parent-child interaction [
5]. Child behavior problems in early regulatory problems include sleep, crying, and feeding or eating difficulties [
6]. A meta-analysis including 22 studies mainly from North America, Europe, and Australia, postulated that about 20% of infants are affected in the first year of life [
7]. They have been associated with various short- and long-term consequences, including impaired self-regulating, social skills, mental health, and parent-child relationships [
7‐
12]. In addition, early regulatory problems were discussed as the earliest indicators of mental health problems in childhood [
13]. Regulatory problems in sleeping, crying, and feeding or eating often co-occur and are interconnected with each other following the triad of symptoms [
5,
6,
14]. For example, sleep problems often involve increased crying in the evening because the child has impaired emotion regulation due to fatigue or expresses protest against going to bed by crying [
1,
5,
6,
15,
16]. Parents often offer food in the form of breastfeeding or bottles as a calming strategy and help to fall asleep, but this makes it more difficult for the child to learn how to fall asleep independently as well as a positive daytime eating routine [
17]. The already increased distress on the parents in the context of a child’s sleeping problems can also increase due to further regulation difficulties, which is expressed in a more tense parent-child interaction, which intensifies the child’s problem behavior [
5]. Sleep, crying, feeding, or eating problems have in common that the child’s self-regulatory competence is not yet sufficiently developed, the parents are overwhelmed and severely stressed, and the parent-child interaction is impaired [
5]. But adequate parental co-regulation in a supportive parent-child interaction is essential to overcome the child’s regulatory problems [
5]. Thus, if the parent-child system is burdened by one regulation problem, it is plausible that child regulation behavior in other domains will also be impaired [
1,
3,
5,
18]. In a German study, multiple regulation disorders affected about 3.4% of children at 12 months of age [
19]. In an Australian longitudinal study of 376 children between two and 24 months of age, 25% of parents reported cry-fuss/sleep problems combined at least once, while they persisted in 6% over at least three-time points [
20]. In infancy as well as in toddler and preschool years, sleep problems are associated with short- and long-term impaired regulatory capacity, which is associated with crying [
4,
15,
21‐
26].
The prevalence of early childhood sleep problems, defined as difficulty falling and staying asleep, difficulty sleeping alone, and bedtime resistance, ranges from 10 to 40% [
20,
27‐
29]. The high effectiveness of behavioral interventions for sleep problems in early childhood in improving children’s sleep has been shown in intervention studies as well as in systematic reviews and meta-analyses of controlled trials and within-subject studies [
30‐
33]. However, to date, no study has shed light on whether sleep interventions may also improve crying and feeding or eating problems.
Childhood crying problems involve unexplainable, unsoothable crying, and in toddlers often goes along with increased crying due to defiance [
6,
34]. Childhood crying problems are often accompanied by high levels of parental distress [
5,
6,
34]. In children between 6 and 47 months, the prevalence of persistent excessive crying is 2.5% [
14]. When parent-reported mild or moderate crying in infancy occurs together with other regulatory problems, the risk of long-term mental health problems is increased [
19]. In toddler and preschool age, the relationship between sleep problems and crying is influenced by the development of the child’s autonomy, resulting in more crying due to defiance, especially as resistance to bedtime, but also due to tiredness during the day [
15,
16,
21,
24,
26,
34].
Feeding or eating difficulties include picky eating behavior, reluctance or refusal to eat, interaction at mealtimes perceived as problematic by parents, and single meals lasting more than 45 minutes [
17,
34]. The prevalence is about 1.4% in the first year and about 3% in the age from 13 to 48 months [
14].
Parental distress describes a parent’s perception of stress about performing the parenting role [
35]. According to the triad of symptoms, parental distress is essential to early childhood regulatory disorders [
5]. Various studies showed associations of increased parental distress with child sleep problems [
36,
37], crying problems [
20,
36], and feeding or eating problems [
36,
38], as well as with the co-occurrence of these regulatory problems [
10,
37,
39‐
41]. Although many studies have focused on maternal distress, there is also evidence that fathers are burdened by a child’s sleep and crying problems [
37,
41].
Different mechanisms could influence children’s sleep, crying, eating behaviors, and parental distress. Since the present study focused on the context of a parent-centered intervention to improve a child’s sleep, several mechanisms are possible. Greater parental knowledge about child sleep and fewer dysfunctional parental cognitions about child sleep behavior are associated with more positive sleep-related parental behaviors, such as good sleep hygiene for the child which is related to improved child sleep [
42]. Since individual parenting strategies for challenging situations particularly include children’s crying episodes in the context of sleep problems, it could be assumed that child’s crying problems may also be reduced if parenting strategies are taught to parents [
32]. A child’s eating problems may decrease with improved sleep hygiene because that includes no longer child’s food intake in the evening and at night as a soothing strategy [
43]. Further, improving infant sleep and regulation problems can lead to a relaxation in parent-child interaction, which is central to a positive eating routine [
5]. In addition, healthy sleep behavior is associated with better emotion and self-regulation in young children which may positively impact crying and eating problems [
3]. Parental distress could decrease through relaxation techniques for parents and a reduction in parental dysfunctional cognitions [
43,
44]. Similarly, improved child sleep and regulation problems could relieve the parental burden and thus contribute to reduced parental distress [
5]. Overall, an interaction between reduced parental distress and reduced child behavior problems may positively impact parent-child interactions, which are central to ameliorating a child’s sleep and regulation problems [
5].
In addition, parents of young children consult professional help mostly due to sleep, crying, and feeding or eating problems [
45,
46]. As the co-occurrence of sleep, crying, and eating problems are highly distressing for parents [
10,
39‐
41], it is also a risk factor for child endangerment, such as shaken baby syndrome [
47,
48]. In addition, the co-occurrence of regulatory problems increases the likelihood of their persistence [
18,
49]. Therefore, early detection and treatment of crying and eating problems in young children affected by sleep disturbances are essential.
The purpose of this study is to investigate the impact of a parent-focused intervention to improve child sleep in individual settings with parents of young children with disturbed sleep. Therefore this study has three main aims: Aim (1) is to assess the impact of the parent-focused intervention to improve child sleep on child sleep (sleep onset latency, frequency and duration of nighttime awakenings, frequency of bed-sharing, and nighttime food intake, total nighttime sleep duration, and sleep efficiency), child crying (frequency of crying episodes, of unexplained and unsoothable crying and of crying out of defiance), child eating difficulties, and parental distress of mothers and fathers. Aim (2) is to assess the maintenance of any changes in these areas longitudinally, at 3-month, 6-month, and 12-month follow-ups. Aim (3) is to explore at the within-subjects level, how children’s sleep, crying, eating, and parental distress changed together across all study measurement points.
Discussion
This pilot study aimed to gain initial insights into young sleep-disturbed children’s sleep, crying and eating patterns, and parental distress in the short- and long-term following a parental sleep intervention and to examine the associations within-subjects between children’s sleep, crying, eating patterns, and parental distress. Based on the data of this pilot study, there could be a trend that children’s sleep disturbances, crying, and eating problems, as well as parental distress of mothers and fathers, reduced after the intervention. However, all results should be interpreted with caution due to the lack of a control group and the high drop-out rate.
Children’s sleep disturbances and crying problems may improve after sleep intervention
The data of this pilot study indicate that child sleep problems improved after intervention with lasting effects for up to 12 months. From pre to post intervention, sleep onset latency decreased from a median of 20 Minutes to 19 Minutes, night waking decreased by one wakeup per night with duration decreasing from a median of 25 Minutes to 12 minutes, resulting in an increase of 16 minutes in total sleep duration and 2 % of sleep efficiency. The median of bed-sharing decreased from 57% of nights to 7 % and nightly food intake from 76% of nights to 22% of nights directly after training. These improvements from pre to post intervention were stable over the follow-up period in almost all sleep parameters. The number of children who suffered from sleep disturbances and sleep disorders decreased after the intervention. These finding are in line with previous research showing the effectiveness of behavioral interventions for sleep problems in early childhood [
30‐
33,
53]. However, this is the first study assessing the effects of the Mini-KiSS intervention in individual instead of group settings, and sheds light on effects in a long-term follow-up period of 12 months. The study results suggest that the Mini-KiSS intervention can also be effective in an individual setting, which would allow for greater flexibility in treatment in a clinical context.
Further, the child crying reduced up to 3 months after the intervention with associations to a reduction of nighttime awakenings and increased sleep efficiency. The frequency of crying episodes decreased after the parent-focused intervention with improvements on the child’s sleep from a median of 1.75 to a median of 1.25, and the frequency of unexplained and unsoothable crying episodes from a median of 2.50 to 2.00, with a value of 1 indicating crying episodes occurred seldom to never and a value of 2 indicating an occurrence of one to three times a week. The decreased frequency of crying and unexplained and unsoothable crying episodes lasted 3 months after the intervention. The number of children whose parents perceived at least mild problematic crying reduced after the intervention. These findings are in line with previous research relating sleep problems with increased crying in young children [
1,
5,
61,
62]. Several aspects could have caused these findings. First, in the sleep intervention, the parents learn to strengthen the child’s self-soothing competence, for example, by practicing falling and staying asleep more independently [
43,
63]. Accordingly, the child relies less on parental co-regulation, which may reduce crying [
5]. Second, the sleep intervention strengthened parental awareness and taught detailed soothing strategies [
43,
64], which may help parents deal adequately with their children’s crying [
65]. However, these findings must be interpreted with caution since no data on crying were available for the children who dropped out of the study. An unexpected finding was that crying due to defiance did not reduce after sleep intervention, although sleep problems were associated in previous research [
15,
24,
66,
67]. It is conceivable that the effect was omitted in the present study because of drop-out bias, small sample size, or parent-reported assessment of crying due to defiance.
Across all measurement timepoints, the frequency of crying episodes decreased together with the reduction of nighttime awakenings. These results confirm and specify previous findings [
22]. There is evidence that reduced nighttime awakenings lead to less fatigue in children, strengthening children’s self-regulatory capacity and may also reduce their crying [
21]. Further, the present results indicate that across all measurement points the frequency of crying episodes decreased together with an increased nightly food intake. To clarify this result, we performed an additional item-level analysis, which showed that this was true only for crying in the morning (
β = − 0.173 [− 0.278--0.069],
F [1, 22.92] = 11.85,
p = .002,
d = 1.43). Since young children compensate for longer intervals without food at night with increased food intake in the morning [
68], hunger could explain increased morning crying. Since sleeping through the night and getting out of the frequent nighttime feeding were issues with the parents [
43], it may be unusual for the children to sleep longer without food. However, across all measurement time points unexplained and unsoothable crying decreased going along with higher sleep efficiency. Previous research found that children’s total sleep duration (an essential part of the sleep efficiency) is related to lower irritability and better self-soothing [
15,
24,
69], suggesting that the child cries less unexplained and soothes more easily. Also crying due to defiance increased across all measurement time points together with lower sleep efficiency. This finding is in line with longitudinal research that postulated a significant correlation between lower sleep percent and behavioral regulation problems [
70]. Further, crying due to defiance increased across all measurement time points together with less bed-sharing with the parents. Since sleeping in the child’s own bed is discussed in the intervention with the parents, this finding could indicate increased defiant behavior if the child was habituated to sleeping in the parent’s bed before the intervention and learns to sleep in their own bed after the intervention. However, surprisingly crying due to defiance decreased across all measurement time points together with more night awakenings. This result contradicts previous findings associated sleep problems with increased tantrums and defiance [
15,
66,
67]. To clarify this finding future research should implement a larger sample and more objectifiable instruments, such as video analysis of an interaction during a clean-up task to assess defiant behavior [
71] and acti- or polysomnography for sleep behavior.
The results indicated a reduction of child eating problems at 3 months after the intervention and an association with a decreased duration of nighttime awakenings. However, eating problems did not significantly reduce directly after the intervention. After 6 months, there was a significant reduction and the number of children whose parents perceived at least mild problematic eating patterns reduced after the intervention. However, these findings are difficult to interpret due to the high drop-out rate. Maybe the late improvement on the eating problem scale indicated no link to the sleep intervention. Also, it should be mentioned that in the studied sample, the eating problems at baseline were not very serious. Future studies should analyze a sample with more clinical eating problems to examine the effectiveness of the sleep intervention. However, the present results indicate that eating problems increased together with a longer duration of nighttime awakenings across all measurement points. This finding is consistent with previous research [
72]. One possible explanation could be that children with eating difficulties often do not eat enough during the day and therefore awake during the night due to hunger or thirst [
72]. The finding that eating problems decrease with progressing time may indicate that the eating problems in the present sample were more transient.
Maternal and paternal distress may reduce after the sleep intervention
In the present study, the parental distress was reduced up to 6 months after the intervention and was associated with decreasing child nighttime awakenings, food intake, and unsoothable crying episodes. The maternal distress decreased significantly directly after the sleep intervention, but this reduction was no longer significant in the follow-up period. In contrast, paternal distress did reduce significantly at three and 6 months after the intervention. A possible explanation could be that maternal distress was reduced more in the sleep intervention because fathers were less involved in sleep-related parenting than mothers in the studied age group [
73‐
75]. Furthermore, the results of the current study are consistent with previous research showing that behavioral sleep intervention for parents with sleep-disturbed children can lead beyond improvements in children’s sleep to reductions in parental distress [
37,
76,
77]. Further, there were not many parents with high levels of parental distress in our sample. The fact that in our sample most parents were only moderately stressed could affect the interpretation of the study results. First, parental ratings of the child’s regulatory behavior might be influenced by the level of parental distress, as they might be perceived as less problematic when parents have lower to moderate levels of distress than when they have high levels of distress. Second, parents with only a moderate level of distress may have a lower willingness to engage in the intervention, which could contribute to the high levels of drop-out in the present study. Third, the study results could be biased if there is a tendency that highly stressed parents remained in the study, and parents with lower levels of distress may be no longer motivated to participate in the follow-up measures. And fourth, the interpretation of the present study results is limited to moderately stressed parents, and we have not yet been able to determine whether the intervention is effective in a sample with highly stressed parents. Evaluating effectiveness in highly stressed parents should be the next step, as in clinical practice high levels of parental distress are often associated with early child regulatory problems. However, the number of parents with high levels of distress reduced after the intervention, but the drop-out rate could also bias this.
The parental distress of mothers increased together with increased child’s nighttime awakenings across all measurement time points, which is in line with previous research [
37]. In contrast, the fathers’ distress across all measurement points increased together with increased nighttime feeding of the child, increased unexplained and unsoothable crying, and reduced time progress. These differences are in line with previous research. It has been shown that fathers were less responsive at bedtime and night than mothers and had more parental tolerance for children’s nighttime crying [
78,
79]. Also, it was assumed that fathers have fewer soothing strategies within their repertoire, which may lead to more difficulties soothing the crying child [
80]. However, Dayton and colleagues [
80] suggest a shift when mothers are weaning the child. Unfortunately, we do not know if the mother or the father did the nighttime feeding in the present study. However, it should be mentioned that differences may relate more to the distinction between the primary and secondary bedtime caregiver than between mothers and fathers [
75]. Future research based on the present study should use separate measurement instruments for both parents to determine which sleep-related parenting tasks are performed by mothers and fathers and to what extent.
The drop-out rate in the present study was very high. However, our results indicated no difference between families who dropped out and families who stayed in the study in terms of demographic variables nor children’s sleep, crying, eating parameters, or parental distress. Parents who dropped out often mentioned reasons like a change in the family situation (e.g., birth, illness, divorce, a move, or job change). Further, it could be that families find it challenging to arrange a fixed appointment over 6 weeks. Subsequent studies could investigate whether drop-out rates can be reduced in a shorter intervention version. However, it is also conceivable that families were no longer motivated to complete the study materials if the sleep problem had improved or because it may have been too difficult for a parent to implement the intervention content alone at home. In both cases, personal contact over the follow-up period could potentially reduce the attrition rate. Because in this study families were contacted only by letter during the follow-up period, a recommendation for future studies would be to seek personal contact again at each measurement time point, for example, in a telephone interview or an additional face-to-face meeting and, if necessary, to provide multiple reminders for any outstanding parent study materials.
Limitations
Several limitations need to be considered. First, a small sample with a substantial attrition rate was analyzed, resulting in some large differences between the analyzed groups. Since unequal sample sizes can lead to a loss of statistical power and an increased Type I error rate [
81] we attempted to mitigate this with the use of Wilcoxon signed-rank tests that analyzed an individual’s repeated measure data as matched pairs which result in equal sample sizes [
56]. For the explorative analyses, we choose the LMM method because it examines the within-subject level and is robust in cases of unbalanced data [
57]. However, the results may not be representative and be influenced by sample selection bias. Second, any comparison to a control group is missing. Therefore, the current study does not provide a sufficient basis to interpret changes in sleeping, crying, and eating patterns and parental distress as a direct effect of Mini-KiSS sleep training. Hence, it is conceivable that the observed changes are related to other factors. The child’s sleep behavior over the study period could be influenced by the normal sleep development or child maturation which can have an impact on sleep behavior like teething [
20,
28]. Third, only subjective and parent-reported data was used, and the crying and eating items were referred to a retrospective assessment. Also, there was no chance to diagnose clinically relevant eating problems in the present study. Future research should include diagnostic interviews at each measurement point in a sample with more clinically relevant crying and eating problems to shed light on a clinically relevant improvement of these regulatory problems after a sleep intervention. Fourth, due to the pilot nature of this study, the LMM analyses were run without
p-value adjustment. In future research, a larger sample with a lower drop-out rate could be achieved through incentives or more telephone contact between follow-up periods. Future studies should include comparison with a control or waitlist control group and more advanced measurement methods, such as 24-hour logs or video analysis for crying and eating patterns and acti- or polysomnography for sleep behavior. However, this pilot study provides preliminary results suggesting that a parent-focused intervention to improve children’s sleep in individual settings may be a promising approach to reduce children’s sleep problems, crying, eating problems, and parental distress. Because early sleep problems are often associated with crying and eating problems and parental distress [
5] clinicians might take away from these study results that a sleep intervention for sleep disturbed children may also have an impact on crying, and eating problems and parental distress, with reductions in the frequency and duration of nighttime awakenings and nighttime food intake and increases in sleep efficiency as the most related factors. The next steps are to validate the present findings in a randomized controlled trial including a larger sample of children affected by clinically relevant sleep, crying, and eating problems, and with parents who suffered from high levels of distress.
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