BACKGROUND: Understanding the effects of SARS-CoV-2 infection and COVID-19 vaccination during pregnancy can help inform clinical guidance and tackle vaccine hesitancy. We examined relationships between SARS-CoV-2 infection during pregnancy, COVID-19 vaccination during pregnancy, and early child developmental concerns in children aged 13-15 months in Scotland. METHODS: We created a large, population-level linked administrative health dataset, combining the COVID-19 in Pregnancy in Scotland (COPS) dataset with age 13-15 month child health review data and other datasets. We included children estimated to have been conceived after May 18, 2020, and born before Sept 30, 2021, and their mothers. We used logistic regression modelling to investigate associations between SARS-CoV-2 infection during pregnancy, COVID-19 vaccination during pregnancy, and developmental concerns (ie, parent or caregiver developmental concerns and health visitor-identified concerns regarding speech-language-communication, problem solving, gross motor, personal-social, and emotional-behavioural development) measured during routine child health reviews at age 13-15 months, including adjustment for confounders and covariates. FINDINGS: A total of 24 919 child-mother pairs (12 752 [51·2%] male children
12 167 [48·8%] female children) were included. 1631 (6·5%) children were prenatally exposed to SARS-CoV-2 and 4943 (19·8%) to COVID-19 vaccination. We found no associations between SARS-CoV-2 infection during pregnancy and developmental concerns. After confounder and covariate adjustment, COVID-19 vaccination during pregnancy was associated with reduced odds of developmental concerns regarding problem solving (odds ratio 0·78 [95% CI 0·64-0·95]), personal-social (0·76 [0·61-0·95]), and emotional-behavioural (0·67 [0·48-0·92]) development, but had no associations with other developmental concerns. INTERPRETATION: SARS-CoV-2 infections during pregnancy do not appear to be linked to early childhood developmental concerns, and COVID-19 vaccinations during pregnancy appear to be safe from the perspective of early childhood developmental concerns. As some developmental concerns do not become apparent until children are older than 13-15 months, future research should continue to monitor outcomes as children grow and develop. FUNDING: Economic and Social Research Council.