Maternal Prenatal Cortisol and Breastfeeding Predict Infant Growth.

Fetal/infant growth affects adult obesity and morbidities/mortality and has been associated with prenatal exposure to cortisol. Bidirectional relations between maternal stress and breastfeeding suggest that they interact to influence offspring growth. No models have tested this hypothesis, particularly regarding longer-term offspring outcomes. We used a subset of the IDAHO Mom Study (n = 19-95) to examine associations among maternal prenatal cortisol (cortisol awakening response (CAR) and area under the curve), and standardized weight-for-length (WLZ) and length-for-age (LAZ) z-scores from birth-18 months, and main and interactive effects of prenatal cortisol and breastfeeding on infant growth from birth-6 months. CAR was negatively associated with LAZ at birth (r = -0.247, p = 0.039) but positively associated at 13-14 months (r = 0.378, p = 0.033), suggesting infant catch-up growth with lower birth weights, likely related to elevated cortisol exposure, continues beyond early infancy. A negative correlation between breastfeeding and 10-month WLZ (r = -0.344, p = 0.037) and LAZ (r = -0.468, p = 0.005) suggests that breastfeeding assists in managing infant growth. WLZ and LAZ increased from birth to 6 months (ps < 0.01), though this was unrelated to interactions between prenatal cortisol and breastfeeding (i.e., no significant moderation), suggesting that other factors played a role, which should be further investigated. Findings add to our understanding of the predictors of infant growth.