Biologic effects of stress and bonding in mother–infant pairs

Objective Maternal stress in humans influences behavior of children and can be assessed using biological markers. Mothers and their one-month-old infants were recruited from an existing study to examine baseline maternal serum oxytocin and hypothalamic-pituitary-adrenal axis response to infant blood heel stick stress as measured by salivary cortisol in the dyads. Objectives were to explore (1) relationships between mother and infant cortisol levels, (2) gender differences in infant biologic cortisol response, and (3) the association of cortisol levels in the dyads and maternal oxytocin levels Methods Forty-two mother–infant dyads provided biologic samples and self-report data. Maternal oxytocin samples were obtained. Initial salivary cortisol was assessed in both the mother and infant, followed by a heel stick blood draw. Twenty minutes later, salivary cortisol was collected again from dyads. Results Self-report measures were negative for depression and risk for childhood neglect. Although oxytocin and baseline cortisol in the infants was higher in mothers that did some breast-feeding, there was no statistically significant difference ( p = 0.2 and p = 0.1, respectively). Analyses showed (a) higher baseline cortisol in mothers was related to higher baseline cortisol in infants ( p ≤ 0.0001), (b) following the stressor, female infants had a larger positive change in cortisol, after adjusting for baseline cortisol ( p = 0.045), and (c) there was no relationship between dyad cortisol levels and maternal oxytocin. Conclusions Maternal and infant biologic stress measures are related. Female infants have a larger hypothalamic-pituitary-adrenal response to a blood draw stressor as measured by salivary cortisol than male infants.