- AIM: To explore the role of breastfeeding as a possible link between maternal and infant cortisol attunement across the first postpartum year. METHODS: Mothers (n = 93) provided salivary samples for cortisol levels over a two-day period during mid-pregnancy and at three, six and 12 months and infants at six and 12 months postpartum. Breastfeeding status was established at these same time points. RESULTS: Among breastfeeding mothers, positive correlations were found between maternal cortisol levels during pregnancy and at three months postpartum and infant cortisol at six or 12 months postpartum. Among nonbreastfeeding mothers, these same maternal and infant cortisol relations were inverse and less pronounced. Further, in breastfeeding mothers, the relationship between maternal prenatal cortisol and infant cortisol at 12 months was mediated through maternal cortisol at three months postpartum. CONCLUSION: These results suggest that maternal cortisol levels are positively associated with cortisol levels of the infant, among mothers who breastfeed. This relationship persists over a one-year period.