The goal of this clinical trial is to find out if person-centered behavioral interventions can help first-time mothers sleep better after childbirth. The study compares two approaches-a behavioral sleep management program and a behavioral aerobic exercise program-to usual postpartum care for women experiencing insomnia symptoms.

The main clinical outcome is insomnia severity. The study also evaluates economic outcomes, including healthcare use, work absenteeism, overall health utility.

Participants will:

• Receive one of the interventions or continue with usual care.
• Keep a sleep diary, a diary on physical activity, and complete questionnaires about sleep, mood, daily functioning, psychosocial factors, and economic outcomes.
• Follow the program instructions, which may include sleep strategies or guided aerobic training, depending on the group.

• The primary objective of this study is to compare the clinical and cost-effectiveness of two behavioural interventions against treatment as usual (TAU) for postpartum women experiencing (sub)clinical insomnia. The study will assess insomnia severity as the primary clinical outcome and healthcare use as the primary economic outcome at six months post-intervention.
• Secondary objectives of this trial are: (1) To define clinical, therapeutic, and sociodemographic factors acting as predictors or moderators for treatment response on insomnia severity in postpartum women. (2) To assess baseline associations between insomnia symptoms, pain, symptoms of depression, and anxiety, and sleep outcomes. (3) To conduct a qualitative process evaluation to explore the experiences and perceptions of participants and intervention providers, as well as examining the underlying mechanisms and contextual factors that influence the effectiveness of the interventions under investigation.
• The primary endpoint was chosen at 6 months follow-up (T3). Other endpoints involve T0 (baseline data), T1 (immediate post-intervention data), and T2 (3 months follow up).
• A total of 135 postpartum women with (sub)clinical insomnia are recruited from community areas around Brussels and Leuven (Belgium) through a combination of community and internet-based strategies. Flyers are distributed across the University Hospitals of Brussels and Leuven, as well as in maternal and child health services, daycare centers, pharmacies, GP waiting rooms, and other key locations frequented by new mothers within a 30 km radius of these cities. Social media advertisements are also placed in relevant parent and perinatal groups. Interested women can contact the research team via phone, email, or a contact form.
• Participants are screened through a phone interview conducted by a researcher not involved in the randomization process. Screening is based on validated questionnaires described in the protocol. Eligible participants receive an informed consent form via email and are instructed to provide a signed copy before enrollment in the study.
• A total of 135 participants are randomized into three groups using block randomization by an independent researcher who is not involved in the trial delivery. To maintain balanced groups, participants are stratified by infant age and insomnia severity.
• Both experimental interventions are delivered by physiotherapists over a six-week period, supplemented with additional materials and a booster call at 3 months post-intervention. The control group receives Treatment as Usual (TAU). After the study concludes, TAU participants are provided with the intervention materials.
• To ensure the fidelity and quality of the delivered interventions, sessions will be audio- or video-recorded with participant permission. A random selection of recordings will be independently reviewed by two researchers using predefined criteria.
• Quantitative data will be collected via web-based self-reported questionnaires using REDCap at T0, T1, T2, and T3. Objective data on sleep and physical activity will also be gathered using wrist-worn actigraphy devices. Recruitment and follow-up require collection of participants' names and contact details. Demographic information is collected at T0.
• Data on therapy dose, adherence, and delivery will be collected through logbooks and recordings. Participants' perceptions of the interventions will be evaluated via surveys and open-ended questions at 3 and 6 months follow-up.
• Handling of missing data: Participants receive automated reminders and personal follow-ups. Appropriate imputation techniques will be used, with likelihood-based estimation assuming data are missing at random.
• Analyzing treatment effectiveness: The primary outcome (insomnia severity) will be analyzed using a linear mixed model. Analyses will follow an intention-to-treat approach. Results will be reported with mean differences, confidence intervals, p-values, and effect sizes.
• Longitudinal daily data will be analyzed with the Group Iterative Multiple Model Estimation (GIMME) approach to capture within- and between-person dynamics.
• Cost-effectiveness and cost-utility analyses will be conducted from a societal perspective, following KCE guidelines.
• Additional explorative analyses and post-hoc analyses will investigate predictors, moderators, and associations between outcomes.
• Process evaluation: Both qualitative and quantitative data will be analyzed to assess intervention fidelity, adherence, and participants' experiences. Findings will be integrated through triangulation to provide a comprehensive understanding of the interventions' impact.
• DATA MANAGEMENT: Data collection and storage will be overseen by the coordinating investigator under supervision of the principal investigators. All questionnaire data will be securely stored in REDCap. Pseudonymized data, logbooks, actigraphy data, and recordings will be stored on secured institutional servers.
• DATA STORAGE: After study completion, all data will be archived in the VUB Institutional Repository and the KU Leuven Research Data Repository for 25 years under restricted access.
• Personal identifiable information (PII) will be assigned unique IDs and stored separately from study data. Only the coordinating team will have access to the identification log. Data will only be shared in pseudonymized or aggregated form.
• Declaration of Helsinki: The trial will adhere to the Declaration of Helsinki, Good Clinical Practice, the protocol, and applicable laws.
• Ethics Committee: Approval of the protocol, informed consent forms, and other relevant documents will be obtained from the applicable ethical committees before the start of the trial.
• Informed Consent: Written informed consent must be provided by each participant prior to any study-related activities.
• Privacy: Data collection and processing will be limited to necessary information, with confidentiality safeguarded according to applicable laws. Participants will be identified only by study numbers in reports and sponsor communications.

Inclusion Criteria:

Women are eligible for study participation if they:

• (1) Have had a singleton pregnancy.
• (2) Are between 4 to 12 months postpartum with their first child.
• (3) Exhibit (sub)clinical insomnia, operationalized as an Insomnia Severity Index (ISI) score greater than 7 7 and having answered 'yes' on the following three statements: a) I have trouble falling asleep, and/or staying asleep and/or I have early morning awakenings AND this causes daytime symptoms. b) My sleeping problem is not caused by an external factor (the baby or my partner). c) These sleeping problems occur at least 3 times a week for at least 3 months.
• (4) Have access to a telephone, computer, and email.
• (5) Possess adequate Dutch literacy to comprehend therapy content, questionnaires, and instructions.

Exclusion Criteria:

Women are excluded from participation if they:

• (1) Are currently pregnant.
• (2) Are shift workers.
• (3) Have severe diagnosed psychopathologies (e.g., bipolar disorder, post-traumatic stress disorder, psychosis)
• (4) Have current severe or untreated sleep disorders (narcolepsy, restless legs syndrome, circadian rhythm disorders)
• (5) Have an unstable medical condition that may disrupt sleep.
• (6) Have received cognitive-behavioural therapy for insomnia (CBTi) within the last 6 months.
• (7) Experience sleep deprivation due to unsettled infant sleep/wake behaviour, defined as the infant waking more than three times per night for more than 30 minutes and requiring parental support to re-initiate sleep.