P153 Sleep timing and chronotype in perinatal periods: Longitudinal changes and associations with wellbeing from pregnancy to 2 years postpartum

INTRODUCTION: Significant changes to sleep occur during perinatal periods. Existing research focuses on sleep duration and quality, but not sleep timing or chronotype. This study investigated change trajectories of sleep timing and chronotype from late pregnancy to two years postpartum, and examined associations between chronotype and insomnia, sleep-related impairment, and mood at seven different perinatal time-points. METHODS: Data were from a 2-arm randomised controlled trial testing behavioural sleep and diet interventions. A community sample of nulliparous females without severe sleep/mental health conditions participated. Participants self-reported bedtime, rise-time, chronotype (short Morningness-Eveningness Questionnaire), Insomnia Severity Index, and PROMIS Depression, Anxiety, and Sleep-Related Impairment over seven time points: gestation weeks 30 and 35, and postpartum months 1.5, 3, 6, 12 and 24. RESULTS: 163 participants (mean age 33.4±3.4 years) took part. Mixed effects models adjusting for age and group allocation showed that both bed- and rise-times became progressively earlier by approximately 20–30 minutes over time (p<.001); chronotype shifted progressively towards more morningness (p<.01). After adjusting for covariates (sleep duration and efficiency, mental health history, social support, age, group allocation), greater morningness was significantly associated with lower symptoms of insomnia and sleep-related impairment over time (p-values<.001); at each time-point, associations between chronotype and symptoms of depression and anxiety were non-significant (p-values>0.65). CONCLUSIONS: Sleep timing and chronotype became progressively earlier over the first two postpartum years. Greater morningness was associated with less sleep complaints and sleep-related daytime impairment during the postpartum period. The mechanisms of these findings may be investigated through further research.