The perinatal period has gained increasing attention from developmental psychopathologists; however, experiences during birth have been minimally examined using this framework. The current study aimed to evaluate longitudinal associations between childhood maltreatment, negative birth experiences, and postpartum mental health across levels of self-reported emotion dysregulation and respiratory sinus arrhythmia (RSA). Expectant mothers (N = 223) participated in a longitudinal study from the third trimester of pregnancy to 7 months postpartum. Participants contributed prenatal resting RSA and completed questionnaires prenatally, 24 hours after birth, and 7 months postpartum. Results indicated that more childhood maltreatment was associated with higher birth fear and postpartum anxiety and depressive symptoms. Resting RSA moderated the association between childhood maltreatment and birth fear, such that more childhood maltreatment and higher resting RSA were associated with increased birth fear. Additionally, self-reported prenatal emotion dysregulation moderated the association between childhood maltreatment and postpartum depressive symptoms, such that more childhood maltreatment and higher emotion dysregulation were associated with increased depressive symptoms. Emotion dysregulation across multiple levels may amplify vulnerability to negative birth experiences and postpartum psychopathology among individuals with childhood maltreatment histories. Thus, emotion dysregulation in the context of trauma-informed care may be worthwhile intervention targets during the perinatal period.