An Investigation of the Evolutionary, Physiological, and Psychological Aspects of Breastfeeding in Mothers of Late Preterm and Early Term Infants

Breast milk is an unparalleled source of nutrition that is particularly beneficial to infants who are born early. Breastfeeding also involves signalling between parent and offspring through biological (breast milk) and non-biological (behavioural) pathways. Maternal stress is one modifiable variable that could influence the signals being transmitted and that could negatively affect breastfeeding success and infant growth. In this thesis, I aimed to investigate the evolutionary, physiological, psychological and behavioural aspects of mother-infant signalling during breastfeeding using an experimental design to improve outcomes among a sample of mothers and their late preterm and early term infants. Maternal stress was manipulated using a relaxation intervention to test whether the intervention would result in stress reduction and higher infant weight gain. Secondary outcomes of the intervention were also studied including infant behaviour (crying, sleeping, appetite), maternal engagement with the infant (responsiveness, attachment), maternal verbal memory, breastfeeding frequency, breast milk volume, and breast milk composition. I also explored whether maternal capital, as an indicator of maternal resources available for investment, is associated with infant outcomes, and whether the relaxation intervention modifies the relationship between these variables. Participants recruited from three hospitals in London were randomised to the intervention group (n=35), where they were asked to listen to a meditation recording while breastfeeding from 3 weeks post-delivery, or the control group (n=37) where no intervention was given. Home visits were conducted at 2-3 weeks and 6-8 weeks post-delivery where information about the mother, infant and breastfeeding was gathered. I also collected breast milk and saliva samples at both times points for macronutrient and hormone analysis. The relaxation intervention was effective in increasing infant weight gain, reducing maternal cortisol, shortening infant crying duration, improving maternal cognitive function and increasing breastfeeding frequency. Maternal capital was associated with infant, maternal and breastfeeding outcomes, and the relaxation therapy modified the relationship between these measures where it was particularly beneficial to mothers of lower maternal capital. Overall, this thesis provides evidence for improving mother-infant signalling using a simple experimental approach in an understudied population and discusses the findings from an anthropological and biological perspective