The Centers for Disease Control and Prevention and the American College of Obstetricians and Gynecologists recommend routine rapid HIV testing in labor and delivery (L&D) for women with undocumented HIV status using an opt-out approach. Identifying factors associated with declining a rapid HIV test in L&D will be helpful in developing strategies to improve rapid HIV testing uptake. Data from the Mother-Infant Rapid Intervention at Delivery study were analyzed. Women ≥24 weeks gestation, in labor, with undocumented HIV status were offered rapid HIV testing using informed consent. Women who declined rapid HIV testing (decliners) but agreed to be interviewed were compared to women who accepted testing (acceptors). 102 decliners and 478 acceptors met inclusion criteria for analysis. Decliners of rapid HIV testing were more likely to have had prenatal care (PNC), after adjusting for age, Hispanic ethnicity, high-school education and city of enrollment (adjusted OR 2.4, 95% CI 1.06-5.58). Having had PNC was collinear with prior HIV education and previous offer of an HIV test during the current pregnancy, so these factors were not part of the model. During PNC, standard informed consent may involve discussions that negatively affect later uptake of testing in L&D. Therefore an opt-out approach to testing may improve testing rates. Furthermore, decliners may have felt that testing in L&D was redundant because of previous testing during PNC; however, if previous testing occurred, this was undocumented at L&D. Documentation and timely communication of HIV status is critical to provide appropriate HIV prophylaxis.