To determine whether African American women expecting their first infant carry a disproportionate burden of posttraumatic stress disorder morbidity, we conducted a comparative analysis of cross-sectional data from the initial psychiatric interview in a prospective cohort study of posttraumatic stress disorder effects on childbearing outcomes. Participants were recruited from maternity clinics in three health systems in the Midwestern USA. Eligibility criteria were being 18 years or older, able to speak English, expecting a first infant, and less than 28 weeks gestation. Telephone interview data was collected from 1,581 women prior to 28 weeks gestation; four declined to answer racial identity items (n = 1,577), 709 women self-identified as African American, 868 women did not. Measures included the Life Stressor Checklist, the National Women's Study Posttraumatic Stress Disorder Module, the Composite International Diagnostic Interview, and the Centers for Disease Control's Perinatal Risk Assessment Monitoring System survey. The 709 African American pregnant women had more trauma exposure, posttraumatic stress disorder symptoms and diagnosis, comorbidity and pregnancy substance use, and had less mental health treatment than 868 non-African Americans. Lifetime prevalence was 24.0% versus 17.1%, respectively (OR = 1.5, p = 0.001). Current prevalence was 13.4% versus 3.5% (OR = 4.3, p < 0.001). Current prevalence of posttraumatic stress disorder (PTSD) was four times higher among African American women. Their risk for PTSD did not differ by sociodemographic status, but was explained by greater trauma exposure. Traumatic stress may be an additional, addressable stress factor in birth outcome disparities.