Background Anxiety in the ante- and postnatal period is prevalent, often co-occurs with depression, and can have adverse consequences for the infant. Therefore, perinatal mental health screening programs should not only focus on depression but also on detecting anxiety. However, in many already implemented perinatal screening programs, adding extra screening instruments is not feasible. We examine the utility of a subscale of the Edinburgh Postnatal Depression Scale (EPDS) consisting of items 3, 4, and 5 (EPDS-3A) for detecting anxiety in new mothers. Methods We used confirmatory factor analysis (CFA) to confirm the presence of the EPDS-3A found in a previous study (n = 320) where exploratory factor analysis (EFA) was used. For the CFA we used a sample of new mothers (n = 442) with children aged 2-11 months recruited from the same population from which mothers for the previous study was recruited. Three models were tested and compared. Receiver operating characteristics of the EPDS-3A were investigated in relation to anxiety caseness status on the combined sample (N = 762). Sample weighing was used to match the dataset to the target population. Cross tabulation was used to investigate the proportion of anxiety cases identified by the EPDS-3A above those identified with the total EPDS. Results The presence of the EPDS-3A was confirmed. An EFA-driven, two-dimensional 7-item model showed the best data fit with one factor representing the anxiety subscale consisting of items 3, 4, and 5. An EPDS-3A score of >= 5 was the most optimal for identifying cases of anxiety (sensitivity: 70.9; specificity: 92.2; AUC: 0.926). Further, we found that the EPDS-3A identifies an additional 2.5% of anxiety cases that would not have been identified with the total EPDS. Conclusions The EPDS-3A can be used as a time-efficient screening for possible anxiety in ante- and postnatal mothers. However, adding the EPDS-3A to routine screening with the total EPDS does not lead to a substantial increase in the number of women identified. In line with previous studies, this study confirms that the EPDS identifies anxiety in addition to depression. Therefore, assessment and treatment adjusted to the specific emotional difficulties is imperative.