Background:Accumulating evidence suggests a persistent impact of perinatal exposure to maternal stress on the infant. In utero, the fetus is particularly vulnerable to maternal stress and mental health complications with various long-term consequences. This study examines the prospective relationship of subclinical maternal perinatal life stress based on individual responses to stressful life events and infant temperament and child development.Methods:Data were derived from the Akershus Birth Cohort, a longitudinal cohort study including 3,752 women scheduled to give birth at Akershus University Hospital, Norway. Psychometric measures pertained to perinatal life stress, maternal perinatal depression (Edinburgh Postnatal Depression Scale), difficult infant temperament at 8 weeks (Infant Characteristics Questionnaire), and child development 2 years after birth (Ages & Stages Questionnaire).Results:Perinatal life stress predicted difficult infant temperament at 8 weeks and challenges in social-emotional development at 2 years above and beyond demographics, pregnancy, and childbirth-related and postpartum factors.Conclusion:Life events perceived as severely distressing in the peripartum period pose a burden on mothers and may have potentially detrimental long-term effects on neurobiological and social-emotional child development. Our findings highlight the need for person-centered perinatal care and support of mothers facing difficult life events. Clinical awareness of in utero development and its relationship to maternal psychological health is warranted to intervene effectively. Future research should consider the timing of in utero exposure and neurobiological and environmental mechanisms pertaining to the relationship between maternal perinatal life stress and child development.