Sleep plays a crucial role in supporting a child's healthy development, growth, and overall well-being. While many children develop healthy sleep patterns, 20-30% of infants experience sleep problems. Beyond biological processes, sleep is influenced by environmental, psychosocial, and cultural factors.

Understanding the relationship between parental factors and child sleep-wake patterns, alongside identifying potential developmental shifts during this period, is essential. However, existing research, often limited to cross-sectional or short-term longitudinal studies, has mostly focused on mothers, with few studies considering the transactional nature between infants' sleep patterns and the bidirectional influences exerted by other important parental factors.

This longitudinal study aims to understand how parent-infant interactions influence infant sleep patterns across the first three years of life for both mothers and fathers. The study will further examine the effects of parental factors, including (1) the co-parenting relationship, (2) maternal self-efficacy, (3) maternal/paternal depression, (4) maternal/paternal anxiety, (5) paternal involvement, (6) maternal/paternal sleep, and (7) parental stress, along with child factors such as temperament and socio-emotional development, on infants' sleep-wake patterns. Additionally, this study will investigate the dynamic, bidirectional relationships between these factors, providing valuable insights into infant and family well-being.

Sleep is a physiological process for a child's healthy development, growth, and well-being. Although child sleep regulation across the early years proceeds well for many, estimates of sleep problems among infants range between 20-30%.

Beyond biological processes, sleep is influenced by environmental, psychosocial, and cultural factors. According to the transactional model, infant sleep is shaped through a bidirectional, continuous, and complex relationship between internal factors related to the infant (such as temperament) and factors related to the parents (such as parental mental health, sleep-related behaviors, and the quality of their relationship with the child). Cultural factors also play a significant role in shaping children's sleep patterns, influencing both their sleep habits and parents' approaches to addressing sleep issues. Understanding how parental factors and child sleep interact and evolve each other during the early years is vital for supporting the well-being of both infants and their families.

The primary objective of this study is to determine how parent-infant interactions influence changes in infant sleep patterns over the first three years of life, enabling the examination of bidirectional linkages and within-person associations between variations in parent and infant sleep. The second objective is to identify predictors of the relationship between parent and child sleep. Moreover, this study will enable the investigators to establish a birth cohort, which will serve as a valuable resource for addressing future research questions and advancing knowledge in this field.

This study adopts a longitudinal, prospective design. Families who are pregnant with first child in the second or third trimester will be invited to participate. Recruitment will take place from January to December 2025. Parents will be followed across seven time points: during pregnancy (second or third trimester) and at 3, 6, 12, 18, 24, and 36 months postpartum.

Sociodemographic information also will be collected. Parents will be assessed by Patient Health Questionnaire-9, Generalized Anxiety Disorder-7, Pittsburgh Sleep Quality Index, Coparenting Relationship Scale, Maternal Self-Efficacy Scale, Parental Stress Scale, Paternal Involvement Questionnaire. Sleep of children will be evaluated by the Turkish version of the expanded brief infant sleep questionnaire and the infant's social and emotional development will be assessed by Brief Infant Toddler Social Emotional Assessment. Child's temperament will be assessed with one question.

Inclusion Criteria:

• Being pregnant with the first child Gestational age>12 weeks Parents over the age 18 Fluent in Turkish Parents living in Istanbul

Exclusion Criteria:

• Suicidal ideation in Patient Health Questionnaire-9 (PHQ-9) No internet access

Healthy pregnant women aged 18 and above and their partners

Requests for wider sharing of data (for example in response to information on Marmara University webpages and in publications about the study and willingness to share), will be addressed on a case-by-case basis. Any data sharing request will be made to investigators through a pre-defined data requisition form. This form will contain information about the applicant, institution, purpose of data request, study objectives, ethical clearance of the study, etc. Once a request has been made the data governance body will discuss if that request was appropriate and meets the criteria set by the university; data will be released following signing of the data sharing agreement. The data will be stored on the Marmara University servers and not be deposited in any 'community' database.