Natural experiments: Disasters and disease outbreaks as models of perinatal hardship and its effects on child brain and behavior.

Human brain development begins in utero and is influenced by the environment. Numerous studies show effects of perinatal maternal psychological distress (e.g., depression) on child brain and behavior. Less attention has been paid to exposure to external real-world stressors (e.g., objective hardship), which are independent of individual characteristics. We systematically reviewed 39 human studies on perinatal maternal stress from natural disasters and disease outbreaks and associations with children's brain structure and function, behavior, and mental health. Studies have mainly focused on the 1998 Quebec Ice Storm or the COVID-19 pandemic, with a handful from other natural disasters. Prenatal maternal objective hardship is related to brain volumes and functional connectivity, though studies have been small and in overlapping samples; no studies to date have examined postnatal maternal objective hardship and brain. Disaster- and disease-related perinatal hardship is related to multiple domains of neurodevelopmental outcomes, including temperament, cognition, and behaviour, with generally negative outcomes (more hardship predicts worse cognition/behaviour). Early gestational exposure is more associated with cognition, though more research is needed to understand windows of vulnerability. The apparent effects of prenatal objective stress on child behavior may occur in part through child brain alterations. Future studies with larger samples are needed, particularly to understand the effects of exposure timing and type, to further investigate sex differences, and to clarify the role of postnatal maternal objective hardship. The COVID-19 pandemic presents a unique opportunity to do this, and several ongoing studies are likely to provide valuable insight in the coming years.