Preterm delivery is a particularly challenging experience that can be experienced by mothers as a traumatic event, causing dissociative reactions and authentic post-traumatic stress disorder (PTSD). In this work, we proposed to study the prevalence of perinatal dissociation and PTSD in mothers of preterm babies compared to a control group of mothers of term babies and to identify factors that may contribute to the occurrence of perinatal dissociation and PTSD following premature childbirth. We conducted a cross-sectional and comparative study, including 97 mothers of premature babies and 80 controls. We used the Perinatal Posttraumatic Stress Disorder Questionnaire to screen for PTSD, the peri-traumatic dissociation questionnaire to measure the level of perinatal dissociation, and the Perinatal Risk Inventory to assess perinatal risk. Compared to mothers of term infants, mothers of preterm infants had significantly higher rates of peri-traumatic dissociation and PTSD. Our results are consistent with previous studies, and add additional credit to the traumatic nature of preterm delivery. Setting up specific support modalities seems essential in the case of premature births in order to ensure a better quality of mother-child interactions and optimal development of the child.