Abstract Objective The goals of the present study were to estimate the incidence and course of full and partial Post-Traumatic Stress Disorder (PTSD) following childbirth and to prospectively identify factors associated with the development of PTSD symptoms at 1 month following childbirth. Methods The sample comprised 308 women, with assessments at four time points: 25–40 weeks gestation, 4–6 weeks postpartum, 3 and 6 months postpartum. Current and prior PTSD were assessed by the Structured Clinical Interview for DSM-IV (SCID-I) and the Modified PTSD Symptom Scale Self-Report (MPSS-SR). Results Incidence rates of PTSD varied according to time of measurement and instrument used, with higher rates of full and partial PTSD using the MPSS-SR at 1 month postpartum (7.6% and 16.6%, respectively). Multivariate logistic regression showed that higher anxiety sensitivity (OR = 1.75; 95% CI = 1.19‒2.57, p = .005), history of sexual trauma (OR = 2.81; 95% CI = 1.07‒7.37, p = .036), a more negative childbirth experience than expected (OR = 0.96; 95% CI = 0.94‒0.98, p = .001), and less available social support at 1 month postpartum (OR = 0.40; 95% CI = 0.17‒0.96, p = .041) independently predicted full or partial PTSD at 1 month following childbirth. Conclusion Our results indicate that a history of sexual trauma and anxiety sensitivity can increase the probability of developing PTSD after childbirth. The findings highlight the importance of screening and providing more tailored services for women at high risk.