We described Medicaid-insured women by receipt of perinatal opioid use disorder (OUD) treatment; and trends and disparities in treatment. Using 2007 to 2012 Medicaid Analytic eXtract data from 45 states and D.C., we identified deliveries among women with OUD. Regressions modeled the association between patient characteristics and receipt of any OUD treatment, medication for OUD (MOUD), and counseling alone during the perinatal period. Rates of any OUD treatment and MOUD for women with perinatal OUD increased over the study period, but trends differed by subgroup. Compared with non-Hispanic White women, Black and American Indian/Alaskan Native (AI/AN) women were less likely to receive any OUD treatment, and Black women were less likely to receive MOUD. Over time, the disparity in receipt of MOUD between Black and White women increased. Overall gains in OUD treatment were driven by improvements in perinatal OUD care for White women and obscured disparities for Black and AI/AN women.