A retrospective cohort study investigated the association between activated partial thromboplastin time (APTT) and septic shock in 1,631 pregnant women with infection admitted from January 2017 to March 2023. Patients were divided into three groups according to APTT: <28 s (n=697), 28–42 s (n=915), and >42 s (n=19). A U-shaped relationship was observed between APTT and the risk of septic shock. The group with APTT >42 s had a higher incidence of septic shock (57.9%) compared to the reference group (11.8%), with an adjusted odds ratio of 3.85 (95% CI 0.94–15.71). The group with APTT <28 s also had an increased risk with an adjusted OR of 1.5 (95% CI 1.02–2.2; p=0.04). Threshold analysis identified 27.564 s as the critical point. Each 1-second increase in APTT increased the risk of shock by 8.7%. APTT monitoring can help assess the risk of obstetric sepsis.