Existing research suggests that childbirth may be a significant trigger of posttraumatic stress disorder (PTSD) in the postpartum period. While literature presents important results regarding the prevalence and risk factors of postpartum PTSD, several gaps remain. The current study examined the factor structure of perinatal PTSD by comparing two supported structures of PTSD. Additionally, structural equation modeling (SEM) was used to examine whether subjective birthing experiences and objective childbirth characteristics mediated the relationship between psychosocial variables (history of trauma, fear of childbirth, and social support) and postpartum PTSD. Women were recruited during pregnancy from the University of Iowa Hospitals and Clinics. Symptoms of PTSD, OCD, and depression, as well as risk factors for postpartum PTSD were measured at pregnancy, 4, 8, and 12 weeks postpartum. Additionally, structured clinical interviews were conducted to assess for depression, PTSD, OCD, and mania. Five factor structures were examined using confirmatory factor analysis, including two four factor models with correlated latent factors, two four factor hierarchical models, and a unidimensional model. All models resulted in adequate global fit and excellent component fit. The most parsimonious model, the unidimensional model was retained. The SEM showed that subjective perceptions of childbirth mediated the relationship between fear of childbirth and postpartum PTSD at 4 weeks postpartum. At 8 weeks postpartum, objective childbirth characteristics mediated the relationship between fear of childbirth and postpartum PTSD and there was a direct relationship between fear of childbirth and postpartum PTSD. The current study supports a hierarchical or unidimensional structure of PTSD in perinatal samples emphasizing the importance of a higher-order, shared dimension of PTSD symptoms. It further emphasizes the importance of fear of childbirth and both subjective and objective birthing experiences in predicting postpartum psychopathology. Future research should examine these symptoms and risk factors in a more diverse and at-risk sample. Additionally, accurate assessments, and influential interventions for postpartum PTSD should be further examined.