Breastfeeding and Kangaroo Care: Biobehavioral
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BREASTFEEDING AND KANGAROO CARE: BIOBEHAVIORAL MEASURES OF DYADIC BONDING, INFANT CORTICAL MATURATION, AND INFANT HPA REACTIVITY by Jillian Hardin A Dissertation Submitted to the Faculty of The Charles E. Schmidt College of Science in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Florida Atlantic University Boca Raton, FL May 2014 Copyright by Jillian Hardin 2014 ii ACKNOWLEDGEMENTS Thank you to my family. I love you all and thank you for your unconditional support throughout this chapter of my life. Special thank you to Mom, Lisa, and Lila for babysitting Averie so I could work. I could never have finished this degree without you, thank you so much! Momma, my accomplishments are a reflection of your loving parenting and guidance. Nana, thank you for your encouragement and all the laughs! Rodney, my sweet husband. You fill my heart with joy each and every day. Thank you for being such a strong positive influence in my life. Thank you for the countless pep talks, helping me through my anxiety attacks, and being the strong foundation of our little family. I admire you more than you’ll ever know. Your mental fortitude, positive attitude, and loving soul are qualities that are unrivaled in anyone else I know. I couldn’t imagine a more fulfilling life. I love having you by my side! Nancy, thank you for everything—your mentorship and support have meant so much to me over the past five years. I can’t thank you enough for being so understanding and helpful when I became a new mom in the middle of my graduate school journey. Your passion for your research is inspiring and I feel so privileged to have had the opportunity to work with you. Thank you to all of the moms and babies who participated in this research. I appreciate you all! Melannie, thanks for all your help. Couldn’t have done this without you. iv ABSTRACT Author: Jillian Hardin Title: Breastfeeding and Kangaroo Care: Biobehavioral Measures of Dyadic Bonding , I n f a n t C o r t i c a l Maturation, and Infant HPA Reactivity Institution: Florida Atlantic University Dissertation Advisor: Dr. Nancy Aaron Jones Degree: Doctor of Philosophy Year: 2014 The current study examined the effects of kangaroo care on breastfeeding practices, infant stress reactivity, and biobehavioral measures of mother-infant bonding across the first 3 months postpartum. Additionally, the role of breastfeeding in infant cortical maturation in the frontal lobe was examined. Thirty two mother-infant dyads participated in the current study; 16 mother-infant dyads were randomly assigned to the kangaroo care group and 17 mother-infant dyads were assigned to the control group. Mothers in the kangaroo care group received training on proper kangaroo care procedures by a trained administrator during the first 1-2 weeks postpartum. Mothers in the kangaroo care group were asked to use the kangaroo care procedure for 1 hour per day for 6 weeks. v Maternal perceptions of fetal attachment, mood, feeding intentions, and urinary oxytocin measurements were assessed prenatally. At a newborn visit, infant neurobehavioral functioning and urinary oxytocin measurements were assessed. Maternal mood and feeding practices were also assessed at the newborn visit. At 3 months postpartum, mother-infant dyads were assessed on urinary oxytocin measurements. Mother-infant dyads were recorded during a play session and feeding session. Infant baseline EEG recordings were taken over a 5 minute period. Infant cortisol measurements were collected from infant saliva before and after a mild behavioral stressor, an infant arm restraint procedure. Maternal perceptions of postpartum bonding, mood, infant temperament, and feeding practices were also assessed. Results indicate that kangaroo care produced medium to large effects on cortisol reactivity, dyadic bonding, and breastfeeding practices if kangaroo care was practiced for the recommended amount of time. Kangaroo care produced medium to large effects on oxytocin levels in mother- infant dyads regardless of use. Cortical measures of infant frontal activity indicated that all infants in the samples displayed functional maturity of the frontal lobe. Kangaroo care can be used a viable, low-cost tactile procedure that can be implemented after birth to aid in breastfeeding practices, mother-infant bonding, and lower infant stress reactivity. Infants in the study who received at least one breastfeeding session displayed advanced patterns of frontal activation. Further study is needed to determine if peripheral oxytocin measurements are 1) reliable and 2) are indicative of dyadic bonding behaviors. vi DEDICATION For my mom, Marianne, and for my daughter, Averie—because motherhood is love incarnate. And for Darius, may you live through all the good I do in life. BREASTFEEDING AND KANGAROO CARE: BIOBEHAVIORAL MEASURES OF DYADIC BONDING, INFANT CORTICAL MATURATION, AND INFANT HPA REACTIVITY List of Tables...........................................................................................................x List of Figures.........................................................................................................xi I.INTRODUCTION.................................................................................................1 Breastfeeding Practices...................................................................................1 Nutritional Benefits of Breastfeeding...................................................2 Cognitive Advantages of Breastfeeding: Direct or Indirect Benefit?...................................................................................6 Neurophysiology of Breastfeeding.................................................................9 Cortisol & Stress.................................................................................12 Attenuation of the HPA axis................................................................15 Gene X Environment Interactions: Considerations to Individual and Group Differences.......................................................16 The Frontal Lobe and Electrophysiological Indices of Neurodevelopment.........................................................................................19 The Influence of Skin-to-Skin Contact on Neurodevelopment, Mother-Infant Bonding, and Breastfeeding Practices...................................24 KC and Maternal Stress.........................................................................26 KC and Infant Outcomes.......................................................................27 The Current Study.........................................................................................29 II. METHOD..........................................................................................................36 Participants....................................................................................................36 viii Materials and Procedure................................................................................37 III. RESULTS........................................................................................................45 Null Hypothesis Significance Testing v. Effect Sizes...................................45 Statistical Analyses........................................................................................46 Results............................................................................................................50 Exploratory Analyses.....................................................................................58 IV.DISCUSSION...................................................................................................60 Electrophysiological Indices of Brain Development, Breastfeeding, Frontal EEG Asymmetry, and Frequency Band Activation..............................................................................................61 Considerations: A Neonatal Sensitive Period for Breastfeeding Benefits?..................................................................................64 Peripheral Oxytocin Measurements in Mother-Infant Dyads...............................................................................................................65 Prenatal Calibration of the HPA Axis.............................................................71 Sensitive Periods: Timing Effects of Kangaroo Care and Breastfeeding...................................................................................................74 Limitations.....................................................................................................79 Exploratory Analysis: Maternal Oxytocin as a Mediator o f t h e R e lationship between Breastfeeding and Maternal Affectionate Care...........................................................................................81 Concluding Remarks.......................................................................................82 APPENDICES........................................................................................................97 REFERENCES....................................................................................................127 ix TABLES Table 1. Dependent Measures of Constructs Assessed at each Visit ..............................82 Table 2. Correlations of Maternal Depression Scales Across Visits ..............................83 Table 3. Means and Standard Deviations of Outcome Measures ....................................84 Table 4. Means and Standard Deviations of Outcome Measures of Groups Based on Kangaroo Care Use ...........................................................................................85