PURPOSE: This study aims to assess rates of COVID-19 exposure during pregnancy among children born during the original, Delta and Omicron waves, and to identify potential disparities. METHODS: This birth cohort includes 125,152 children born from 3/1/2020 to 2/28/2023 in southern California. Data on maternal COVID-19 infection, demographics, and health status were extracted from electronic medical records. Rates were calculated for each wave and subgroup. Poisson regression tested trends over waves and compared rates within each subgroup. RESULTS: A total of 20,187 (16.1%) children were born to mothers with COVID-19 during pregnancy. Rates were 2.8%, 13.6% and 26.5% during the original, Delta and Omicron waves respectively (p<0.0001). Younger mothers (age <25 and 25-35 years) had higher rates during the original and Delta waves but not during Omicron. Children of Black women had 47% higher rates during the original wave; and children of Hispanic women had 156% and 81% higher rates during the original and Delta waves, respectively. No significant differences were observed for Omicron. Higher neighbourhood deprivation index and Medicaid insurance had higher rates during the original and Delta waves. Higher maternal parity and obesity were associated with higher rates in all waves, with greater disparities during the original and Delta waves. Maternal diabetes, asthma or autoimmune disease were associated with higher rates during the Omicron wave. CONCLUSION: Substantial disparities exist for COVID-19 exposure during the original and Delta waves, but not for Omicron. These findings are important for public health and future research.