Mother-infant circadian rhythm: development of individual patterns and dyadic synchrony.

Background: Mutual circadian rhythm is an early and essential component in the development of maternal-infant physiological synchrony.
Aims: The aim of this to examine the longitudinal pattern of maternal-infant circadian rhythm and rhythm synchrony as measured by rhythm parameters.
Study Design: In-home dyadic actigraphy monitoring at infant age 4, 8, and 12 weeks.
Subjects: Forty-three healthy mother-infant pairs.
Outcome Measures: Circadian parameters derived from cosinor and non-parametric analysis including mesor, magnitude, acrophase, L5 and M10 midpoints (midpoint of lowest 5 and highest 10h of activity), amplitude, interdaily stability (IS), and intradaily variability (IV).
Results: Mothers experienced early disruption of circadian rhythm, with re-establishment of rhythm over time. Significant time effects were noted in increasing maternal magnitude, amplitude, and IS and decreasing IV (p<.001). Infants demonstrated a developmental trajectory of circadian pattern with significant time effects for increasing mesor, magnitude, amplitude, L5, IS, and IV (p<.001). By 12 weeks, infant phase advancement was evidenced by mean acrophase and M10 midpoint occurring 60 and 43 min (respectively) earlier than at 4 weeks. While maternal acrophase remained consistent over time, infants became increasingly phase advanced relative to mother and mean infant acrophase at 12 weeks occurred 60 min before mother. Mother-infant synchrony was evidenced in increasing correspondence of acrophase at 12 weeks (r=0.704), L5 (r=0.453) and M10 (r=0.479) midpoints.
Conclusions: Development of mother-infant synchrony reflects shared elements of circadian rhythm.
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