Across the perinatal transition, existing research focuses mainly on significant changes in sleep duration and quality, neglecting sleep timing. This study investigated change trajectories of sleep timing and chronotype from late pregnancy to 2 years postpartum and examined longitudinal associations of chronotype with symptoms of insomnia, daytime sleep-related impairment, and mood. Data were from a two-arm randomised controlled trial testing parent-focused wellbeing interventions. Participants were a community sample of nullipara without severe sleep/mental health conditions. Participants self-reported bedtime, rise-time, chronotype, insomnia symptoms, sleep-related impairment, depression, and anxiety at seven time points: gestation Weeks 30 and 35, and postpartum Months 1.5, 3, 6, 12 and 24. Trajectories were estimated using mixed-effects models with continuous time, quadratic splines, and a knot at childbirth, controlling for age and group allocation. A total of 163 participants (mean [SD] age 33.35 [3.42] years) took part. Bedtime and rise-times delayed during late pregnancy (~8 and ~20 min, respectively) but became progressively earlier (~20 and ~60 min, respectively) over the 2 postpartum years. Chronotype became more eveningness in late pregnancy, and more morningness after childbirth, however changes were small. Controlling for sleep duration and efficiency, greater morningness was associated with significantly less symptoms of insomnia and sleep-related impairment over time (all p < 0.001); longitudinal associations between chronotype and symptoms of depression and anxiety were non-significant (all p > 0.65). Sleep-wake timing and chronotype became progressively earlier from pregnancy to 2 years postpartum. Morningness chronotype may be sleep-protective during the transition from pregnancy to parenthood. Mechanisms underlying these associations require further research.
