Existing literature on maternal distress has focused on stress and anxiety during the pregnancy or postnatally and their relationship with child development. However, few studies have investigated the association between maternal stress and anxiety symptoms over time and child development in preschool children. The aim of this study was to examine the association between trajectories of maternal stress and anxiety symptoms from mid-pregnancy to three years postpartum and child development at age three years.Data were analyzed from 1983 mother-child dyads who participated in the three year follow-up of the All Our Families (AOF) study. Latent class analysis (LCA) was conducted to identify trajectories of women's stress and anxiety across from mid-pregnancy to three years postpartum. Multivariate logistic regression was used to explore the relationship between the stress and anxiety trajectories and child developmental delays while adjusting for the covariates.LCA identified three distinct trajectories of maternal stress and anxiety symptoms over time. Multivariate analysis showed mothers assigned to the high anxiety symptoms class had an increased risk (adjusted OR 2.80, 95% CI 2.80 (1.42 ─ 5.51), p = 0.003) of having a child with developmental delays at 3 years.The use of self-reported maternal mental health symptoms and no data on fathers' mental health are our study's limitations.The findings from a population-based Canadian sample provide empirical support for a relationship between maternal anxiety overtime and risk of child developmental delays. Identifying and supporting mothers experiencing high anxiety symptoms in the perinatal period may mitigate the risk of these delays in children.