Background: Post-traumatic stress disorder (PTSD) affects approximately 3% of women in the postnatal period, but less is known about risk factors for PTSD than other postnatal mental illnesses. This review aimed to analyze the literature on the impact of mode of birth on postnatal PTSD. Methods: Searches were undertaken of CINAHL, the Cochrane Library, MEDLINE, PsycINFO, and Scopus for studies investigating the link between mode of birth and postnatal PTSD in high-resource countries from January 1990 to February 2021. Quantitative and qualitative data were collected and synthesized. Meta-analysis was performed with four of the studies, and the rest were analyzed narratively. Results: Twelve quantitative studies, presenting data on 5567 women, and two qualitative studies, with 92 women, were included in the review. Most studies found a significant relationship between mode of birth and maternal PTSD symptoms. Meta-analysis found cesarean birth was more closely associated with PTSD than vaginal delivery (VD) (P = 0.005), emergency cesarean birth (EmCB) more than elective cesarean birth (ElCB) (P < 0.001), instrumental vaginal delivery (IVD) more than spontaneous vaginal delivery (SVD) (P < 0.001), and EmCB more than SVD (P < 0.001). Women who developed PTSD after EmCB felt less in control and less supported than those who did not develop it after the same procedure. Request for repeat ElCB appeared more common among women with pre-existing postnatal PTSD, but this may subsequently leave them feeling dissatisfied and their fears of childbirth unresolved. Conclusions: Modes of birth involving emergency intervention may be risk factors for the development of postnatal PTSD. Ensuring that women feel supported and in control during emergency obstetric interventions may mediate against this risk.