PRENATAL AND EARLY POSTNATAL STRESS
Prenatal stress affects behavior and development of the offspring. Monkeys born to mothers stressed during pregnancy (e.g. exposed to unpredictable noises in a dark room) show decreased motor and exploratory behaviors, reduced cognitive ability, and delayed mastery of object permanence. Similarly, children whose mothers were stressed during pregnancy have less optimal outcomes, including problems with emotional regulation, motor delays, and intrauterine growth retardation.
Prenatal exposure to excess glucocorticoids (a hormone that predominantly affects the metabolism of carbohydrates and, to a lesser extent, fats and proteins) may harm the developing brain. Offspring of prenatally stressed rat or monkey mothers have increased basal levels of plasma ACTH (adrenocorticotropic hormone, stimulates the adrenal cortex), increased ACTH in response to stressful situations, and decreased ability to adapt to ongoing stress. Human infants born to mothers with prenatal depression tend to be less active, less socially responsive, and fussier than unexposed peers, possibly via the same pathway.
The possibility of "multigenerational effects" of stress has been suggested by animal studies. Infants prenatally exposed to stress have small heads; infants with small heads have abnormal stress responses. Non-optimal birth conditions (microcephaly, +/- low Apgar scores) are associated with abnormal stress responses for at least the first six months of life.