Effects of White Noise and Lullaby on Vital Signs of Term Newborns in Neonatal Intensive Care

Background and Rationale: Newborns admitted to the Neonatal Intensive Care Unit (NICU) are frequently exposed to environmental stressors that may disrupt autonomic stability. Developmental care strategies increasingly incorporate sensory modulation approaches to support physiological regulation. Auditory stimulation, including white noise and lullabies, has shown potential to reduce stress responses and promote behavioral organization. However, comparative evidence in term newborns remains limited, as most studies have focused on preterm populations. This study was designed to evaluate and compare the short-term physiological effects of two standardized auditory interventions-white noise and lullaby exposure-in term newborns under controlled NICU conditions. Study Design and Setting: This was a prospective, multicenter, parallel-group randomized controlled trial conducted in two tertiary NICUs in Türkiye. Participants were randomized in a 1:1 ratio using stratified block randomization by center, with allocation concealment ensured through sealed opaque envelopes. Intervention Protocols: Both interventions were delivered in a standardized manner to minimize environmental variability. Auditory stimulation sessions lasted 20 minutes and were administered three times daily over four consecutive days. Sound intensity was calibrated prior to each session and maintained below 55 dBA to ensure auditory safety. White noise exposure consisted of a digitally standardized recording simulating intrauterine acoustic patterns. The lullaby intervention consisted of a culturally familiar, standardized digital recording. All sessions were conducted during stable clinical conditions and scheduled to avoid routine caregiving activities. The playback device was a portable MP3 player with a 3-5 W speaker placed approximately 50 cm from the infant's ear. Sound intensity was measured before each session using a Wintact WT85 decibel meter, maintaining a maximum of 55 dBA (A-weighted). Sessions were conducted during quiet periods after routine care and feeding to minimize external stressors. Data Collection and Measurements: Physiological parameters were obtained using continuous bedside monitoring systems. Heart rate and oxygen saturation were automatically recorded, while respiratory rate was assessed using standardized observation methods. Repeated measurements within sessions enabled evaluation of temporal trends and within-subject variability. Statistical Analysis: The primary analytical approach utilized linear mixed-effects models to account for repeated measurements within individuals. Fixed effects included intervention group, time, and group-by-time interaction, while random intercepts accounted for within-subject correlation. Baseline values and study center were included as covariates. Sensitivity analyses were performed to assess the robustness of the findings. Ethical Considerations: The study was approved by the institutional ethics committee, and written informed consent was obtained from parents or legal guardians prior to enrollment. All procedures were conducted in accordance with the Declaration of Helsinki.