ObjectiveTo compare a general anxiety instrument plus a depression instrument with a specific postpartum anxiety instrument plus a depression instrument to detect postpartum anxiety and to explore trends in daily postpartum anxiety. DesignProspective, longitudinal cohort study. SettingAcademic tertiary center in the mid-Atlantic United States. Study activities were remote. ParticipantsPregnant women (N = 73) in the third trimester of pregnancy. MethodsWe administered the State–Trait Anxiety Inventory (STAI), Postpartum Specific Anxiety Scale (PSAS), and Edinburgh Postnatal Depression Scale (EPDS) at 1 and 8 weeks after birth. We used mobile ecological momentary assessment prompts to measure daily anxiety levels (0–10) from 1 to 8 weeks after birth. We defined the presence of anxiety and depression by using the established instrument cutoff scores. We used repeated-measures analysis of variance and dependent-samples t tests to determine the stability of the determined anxiety instruments during the study time frame. We used linear mixed modeling to explore mobile ecological momentary assessment anxiety trends. ResultsThe PSAS and EPDS detected more participants with anxiety and/or depression (26.8%, 19/71) than the STAI and EPDS (23.9%, 17/71) at 8 weeks after birth. PSAS scores increased from 1 to 8 weeks after birth (p = .003); STAI scores decreased (p = .01). Daily anxiety ratings changed nonlinearly during the study period, were greatest at 2 weeks, declined and stabilized, and then trended upward toward Week 8. ConclusionDetection of postpartum anxiety in clinical settings can be improved through addition of the PSAS in routine screening. Timing of anxiety assessment should be considered between 6 to 8 weeks after birth.