Effects of Daily Skin-to-Skin Contact on Full-Term Infants’ Cortisol Reactivity and Mother-Infant Synchrony

• In Event: Understanding Dyadic Biobehavioral Synchrony: Developmental Precursors and Functions

Abstract

Introduction. During Skin-to-skin contact (SSC), mothers place their infant on their bare chest (WHO, 2003). Regular SSC has been related to beneficial outcomes for infants’ health and well-being. Body contact is suggested to permit mothers to regulate infants’ physical and behavioral processes. The physical proximity, face-to-face exchanges and tactile interactions can also foster bio-behavioral synchrony. Accordingly, regular SSC has been related to decreased cortisol reactivity during a stressor in the only study on effects of long-term SSC on cortisol reactivity in full-term infants and to synchronisation of cortisol levels between mothers and their premature infants. Effects of SSC on synchrony between mothers and full-term infants have never been assessed. This randomized controlled trial hypothesises that daily SSC in full-term infants: a) decreases infants’ cortisol reactivity to a stressor; and b) increases adrenocortical synchrony between mothers and infants.
Methods. We randomly allocated 116 mother-infant dyads to a SSC or control condition. Mothers in the SSC condition were instructed to perform one hour of SSC per day throughout the first five weeks after birth. Mothers recorded their daily amount of SSC in a diary. In week six, mothers bathed their infants during a home-visit. Bathing reliably produces increases of cortisol in infants (Albers et al., 2008). Salivary cortisol was assessed from mothers and infants before, as well as 25 and 40 minutes after the bath. The data were analyzed using multilevel growth curve modelling. Hypothesis one was tested by looking at the effect of condition and the interaction of condition with time (baseline, post-stressor, recovery on infant cortisol). Hypothesis two was tested in a separate model, looking at the interaction effect of mothers’ cortisol with condition on infant cortisol. For both hypotheses, three types of analyses were performed: intention-to-treat (ITT), per protocol (PP), and exploratory dose-response (DR) analyses.
Results. Hypothesis 1. The effect of condition (SSC vs. control) on infant cortisol was not significant in any analysis. A main effect of quadratic time was found in all analyses (see Figure 1). Since the interaction between condition and time worsened the fit, it was not included in the final models. Hypothesis 2. The interaction effect of mothers’ cortisol with condition on infant cortisol tended towards significance in the ITT and the PP analysis (see Figure 2). While infant cortisol did not follow maternal cortisol in the SSC condition, there was a tendency for a negative association between both in the control group.
Conclusion. The hypothesized effect of SSC on infant cortisol reactivity was not found and support for mother-infant synchrony was weak. This might indicate that regular SSC does not affect cortisol reactivity of 6-week-old infants. Another reason for these null results could have been the low compliance with requested amounts of SSC and the consequently small sample in the per protocol analysis. Further research should also assess potential effects of regular SSC on behavioral synchrony, as well as other stress-related indicators such as crying behavior.

Authors

• Nicole Rheinheimer, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center
  Presenting Author

• Hellen Lustermans, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center
  Non-Presenting Author

• Kelly Cooijmans, Behavioural Science Institute, Radboud University
  Non-Presenting Author

• Roseriet Beijers, Radboud University
  Non-Presenting Author

• Carolina de Weerth, Radboud University Medical Center
  Non-Presenting Author