Timing of Prenatal Stress Exposure Predicts Infant Sympathetic Nervous System and Affective Responses.

Prenatal stress has broad detrimental consequences for neurodevelopment, with potential sensitive periods within gestation affecting specific developmental systems. We examined the effects of prenatal stress timing, level, and fluctuations on three markers of sympathetic nervous system activity: infant salivary alpha amylase (sAA), fear, and anger responses. In addition, we explored whether the effects of prenatal stress differed for boys and girls. We assessed 195 mother-infant dyads (45% girls) from an ethnically diverse and economically disadvantaged community sample. Women reported perceived stress weekly from gestational week 14 to delivery. Dyads completed 6-month postpartum in-person assessments in which infants' behavioral responses to two stressful tasks were coded and saliva collected. Machine learning analyses revealed that sAA and fear responses were predicted by increases in stress during the early third trimester (31-32 weeks) while increases in stress levels during mid- (21 weeks) and late-gestation (38 weeks) predicted lower anger in response to a frustration task. Sex-specific analyses pointed to different sensitive periods for boys and girls. Our findings emphasize the importance of collecting granular data during pregnancy to identify the epochs during which stress exposure is most pernicious, as well as the usefulness of assessing multiple indicators of infant biobehavioral reactivity to better capture the full toll of prenatal stress exposure.