Breastfeeding can be described as a two-person, single-organ system. Infant suckling stimulates production of both oxytocin and prolactin, and infant demand drives milk supply. If the breast is not emptied regularly, engorgement occurs, downregulating prolactin receptors in the mammary epithelium and reducing milk production.83
Successful lactation, therefore, requires mature infant suck-swallow patterns; maternal depression may affect this oromotor development. Exposure to elevated CRH during pregnancy has been linked with differences in neurologic maturation84
and neuromuscular development.85
At birth, neonates born to depressed mothers exhibit different suckling responses than those born to euthymic mothers.86
Maternal depression may also affect breastfeeding outcomes via its influence, in utero
, on physiologic processes that underlie developing infant temperament and behavior. Maternal depression during pregnancy may have a profound effect on offspring development.87
For example, maternal psychologic symptoms lead to distinguishable differences in fetal heart rate response to stress by the end of pregnancy,88
such that fetuses of more anxious mothers showed significant increases in heart rate during a stressor, whereas fetuses of less anxious mothers showed nonsignificant decreases in heart rate. Thus, even before birth, fetuses of more anxious mothers show greater stress reactivity than those of nonanxious mothers.
These differences continue to be observed after birth. Infants of depressed mothers have physiologic and biochemical profiles that mimic their mothers during pregnancy, including lower levels of dopamine and serotonin, elevated norepinephrine and cortisol, and greater relative right frontal electroencephalogram (EEG).89–91
In addition, elevated maternal depressive symptoms during pregnancy are related to lower vagal tone in newborns90
and in 3–6-month-old infants at rest and during interactions with their mothers.92,93
Taken together, these results suggest that infants of depressed mothers may develop maladaptive biobehavioral regulatory patterns, which are known to underlie characteristics associated with negative temperament.
One of the most extensively studied physiologic pathways from maternal depression in utero
to infant outcomes is placental CRH (pCRH). In some94,95
but not all96
studies, midpregnancy pCRH has been found to be an early predictor of postpartum and prenatal depression. pCRH has also been associated with preterm labor, reduced birth weight, and slow growth rate in infants.97–101
High late-pregnancy cortisol levels are also associated with increased crying, fussing, and negative reactivity and facial expressions in infants, as well as maternal ratings of more difficult temperament.102,103
The role of infant temperament in feeding outcomes is not well understood, but there is evidence of a relationship between difficult temperament and reduced breastfeeding during the first half-year of life.104,105
Jones et al.106
assessed maternal-infant behavior and development in cohorts of depressed and nondepressed women who were breastfeeding and bottle-feeding, and they concluded that maternal depression affects both infant temperament and infant EEG asymmetry, which, in turn, reduced breastfeeding duration. Thus, gestation in the setting of maternal depression or anxiety may impact infant development, leading to breastfeeding difficulties and early weaning.