In 1992, Abidin defined parenting stress as the parental perception that the demands placed by their children outstrip their resources.1 This form of stress may stem from feelings of deep sadness or anxiety in parents, dysfunctional parent-child interaction patterns, lack of social support, distorted parental subjective perceptions or difficulties of the child in daily living.2,3 Neurodevelopmental outcomes in children are closely associated with the relationship they develop with their parents, as the parent-child bond combined with adequate parenting skills can promote adequate self-regulation and secure attachment in the child.4

It is estimated that 5%–10% of parents may experience high levels of stress or burnout in their parenting role.5 There is evidence of an association between high parental stress and more rigid and strict parenting styles, decreased parent-child interaction and an increased probability of child maltreatment.6 Parental stress is also associated with an increased risk of attention-deficit/hyperactivity disorder, language or mood disorders or social/behavioral problems in the child.7,8

On the other hand, sleep disorders are a common and relatively underestimated condition in children and have been found to be associated with cognitive, behavioral, emotional, physical and social interaction difficulties. In the International Classification of Sleep Disorders, Third Edition (ICSD-3), the American Academy of Sleep Medicine defines insomnia as difficulty initiating or maintaining sleep or nonrestorative sleep despite adequate circumstances for sleep and causing distress or daytime impairment.9 It is estimated that 30% of children aged 6 months to 5 years experience insomnia.10 The important of sleep at age 2 years is evinced by the impact of nighttime sleep duration on socioemotional development in toddlers or the predisposition to attention-deficit/hyperactivity disorder and delay in language acquisition associated with irregular sleep deprivation.11 It is believed that from age 2 years, there is a transition in the functions of sleep from neural reorganization to neural repair and metabolite clearance.12

Stress and sleep problems are conditions with a bidirectional association, and there is evidence that stress may result in a reduction in sleep duration and quality while insomnia can cause an increase in cortisol levels.13 Sleep arrangements in the household can affect the functioning and stress of the family.14,15

In light of the above, the main objective of our study was to determine the association between toddler sleep quality at age 2 years and parental stress. As secondary objectives, we analyzed the association between parental stress and variables related to sleep habits, such as co-sleeping, as well as demographic factors such as parental age, the presence of siblings and household socioeconomic status.

The sample included 109 families, of which 53.2% brought in a daughter and 46.7% a son. In 44% of cases, the mother completed the questionnaires, in 21.1% it was the father, and in 34.8% both parents did it together. A total of 25 families reported co-sleeping (22.9%), 16 (14.6%) reported sharing the bedroom without co-sleeping and 68 (62.3%) reported that the child slept in another room.

When it came to the toddler’s sleep, the median and interquartile range values were 500min (447.5–602.5) for the total nighttime sleep duration, 15min (5–60) for the time spent awake during the night, 1 (0–3) for the number of nighttime awakenings and 10min (8–20) for the time it took the child to fall asleep. The mean total score in the PSI-4-SF was 61.1 (SD, 12.3), while the mean subscale scores were 23.8 (SD, 3.2) for parental distress, 20.2 (SD, 3.9) for parent-child dysfunctional interaction and 21.5 (SD, 3.1) for difficult child.

The correlation coefficient (r) and coefficient of determination (R2) obtained for the correlation between the total PSI-4-SF score and the minutes of nighttime sleep, the minutes awake at night, the number of nighttime awakenings and the minutes of sleep latency were −0.478 (P=.001), R2=0.22; −0.237 (P=.07), R2=0.05; −0.344 (P=.005), R2=0.11 and −0.205 (P=.09), R2=0.05, respectively.

Table 1 presents the total and subscale scores in the PSI-4-SF in relation to whether the total nighttime sleep duration of the child was greater than or less than 540min.

Table 2 presents the PSI-4-SF scores in relation to sleep and feeding practices and sociodemographic characteristics.

Co-sleeping was associated with breastfeeding maintenance at age 2 years (odds ratio, 18.4; 95% CI, 5.9–56.8). We did not find a statistical association between co-sleeping and pacifier use, parental age, child sex, presence of siblings or socioeconomic status.

Table 3 describes the differences in minutes of nighttime sleep, minutes awake at night, number of awakenings, and minutes to fall asleep in relation to the practice of co-sleeping.

Parental stress increased with decreasing nighttime sleep duration in toddlers and with co-sleeping at age 2 years, as well as with a mean parental age of less than 20 or more than 40 years. On the other hand, co-sleeping was associated with a reduced duration of nighttime sleep, an increase in the time awake at night and more awakenings. To our knowledge, this is the first study that analyzes the association between parental stress, toddler sleep and co-sleeping at age 2 years.

As would be expected, parents of children with nighttime sleep problems report increased daytime somnolence affecting their daily lives, which translates to a negative perception of parenting in association with insufficient maternal sleep as well as higher levels of stress.21,22 This phenomenon is more prominent in mothers than in fathers, and infant sleep has been found to be a predictor of maternal sleep quality, mood, stress and fatigue.23 There is evidence suggesting that maternal mental health is associated with the perceived toddlers sleep quantity and quality, and that this association is mediated by maternal sleep duration.24 De Stasio et al. described the effect of the number of toddler nighttime awakenings on maternal stress, while paternal stress was more affected by the time required by toddlers to fall asleep.15 Our findings on the increase in parental stress in association with a reduced nighttime sleep duration in toddlers corroborated the results published by Tikotzky et al. and by Merril and Slavik, who reported higher levels of parental stress (measured with different methods) in association with sleep disturbances in the offspring, from the birth of the child, throughout childhood and even up to age 25 years.25,26

When we analyzed the subscales of the PSI-4-SF, we found differences in the parent-child dysfunctional interaction and the difficult child subscale scores based on the total minutes of nighttime sleep, based on which we may infer that the child’s insomnia has a more negative impact on the parent-child bond, parental expectations and parental perception of the child as problematic, with a lesser impact on the quality of the couple’s relationship or the perceived limitations in everyday life associated with parenting. These results support previous findings regarding improved parental perception of having a difficult child as well as more secure attachment of the toddler in relation to increased duration of nighttime sleep in the child.27,28

Parental age was the only analyzed socioeconomic factor that had a negative impact on parental stress. Individuals who become parents at an early age (due to inexperience, financial difficulties, etc) or at an advanced age (more or more serious health concerns, higher rate of postpartum depression) are more likely to experience higher levels of stress.29,30 We did not find evidence of socioeconomic status affecting stress, an association reported by other research groups in both developed and developing countries, probably attributable to the difference in the number of stressors, such as material difficulties and limited social support.31,32

Our results regarding the increase in parental stress associated with co-sleeping corroborate the findings of the study conducted in infants aged 3–6 months by Teti et al., who reported greater coparenting distress and less emotionally available mothering in families that co-slept.33 On the other hand, co-sleeping reinforces the negative association between decreased maternal sleep and perceived toddler sleep problems.24 It must be taken into account that our study assessed the impact of co-sleeping at a later stage (age 2 years), when the percentage of families that co-sleep is lower compared to earlier stages: 22.9%, slightly lower compared to the rate reported in Spain at age 1year (26%), with the only reported percentage for age 2 years (43.6%) corresponding to a study conducted in China.34,35 Furthermore, it is believed that the emotional state of parents returns to the pregestational baseline by two years post birth, making this a more appropriate time for the emotional assessment of parents.36

The reason that motivated the decision to co-sleep should be considered, for, if the choice to co-sleep was based on previous sleep problems in the child, the increase in parental stress could be due to the child’s insomnia, which would warrant the exclusion of the family from the study. In addition, co-sleeping could increase parental awareness of the toddler’s potential awakenings due to the increased physical proximity compared to the child sleeping in a different room, and it can also be a source of conflict between partners, thereby increasing parental stress.37 Still, there is evidence of a paradoxical decrease in the awareness of sleep problems in the offspring among caregivers who co-sleep with their toddler at age 2 years, despite evidence of a shorter sleep duration in these children.35

The impact of co-sleeping on children's sleep is a controversial subject, with published studies yielding heterogeneous results; polysomnography data have evinced a decreased duration of stages 3 and 4 of sleep and an increased duration of stages 1 and 2 of non-REM sleep in infants who co-sleep, but there is still no consensus among authors as to whether co-sleeping increases, decreases (as found in our study), or has no effect on the quality and quantity of children’s sleep.38–40

The data presented in this article are novel in that they analyze parental stress at a time for which there is a dearth of evidence (when the child is aged 2 years), linking parental stress to toddler sleep quality and sleep practices in the family. We found no studies in the literature examining the association between parental stress and co-sleeping at this age. Furthermore, the tool we used to measure parental stress (PSI-4-SF), which is universally used, validated, and easily accessible, has not been used in similar studies. Among the limitations of the study, we ought to highlight the assessment of sleep, in which no objective measures (such as actigraphy) were used, the potential bias in the detection of reduced sleep duration in children stemming from parental schedules and/or daycare attendance, even if parents were directed to consider nights when sleep would not be restricted on account of external factors, and the potential for participation bias, as families who experience problems related to their children’s sleep may be more willing to participate in a survey that assesses this aspect.

In conclusion, the findings of the study support a strong association between reduced child sleep duration at age 2 years and increased parental stress. In addition, the practice of co-sleeping was associated with increased parental stress and decreased sleep duration in the child. Extreme parental age (whether young or old) was also associated with a higher level of stress

This research did not receive any external funding.