Anxiety affects around one in five women during pregnancy and after birth. However, there is no systematic information on the proportion of women with perinatal anxiety disorders who want or receive treatment.

To examine (a) the prevalence of anxiety disorders during pregnancy and after birth in a population-based sample, and (b) the proportion of women with anxiety disorders who want treatment and receive treatment.

This study conducted 403 diagnostic interviews in early pregnancy (n = 102), mid-pregnancy (n = 99), late pregnancy (n = 102) or postpartum (n = 100). Participants also completed self-report measures of previous/current mental health problems and desire for treatment at every time point.

The prevalence of anxiety disorders over all time points combined was 19.9% (95% CI 16.1–24.1), with greatest prevalence in early pregnancy (25.5%, 95% CI 17.4–35.1). The most prevalent disorders were obsessive–compulsive disorder (8.2%, 95% CI 5.7–11.3) and generalised anxiety disorder (5.7%, 95% CI 3.7–8.4). The majority of women with anxiety disorders did not want professional help or treatment (79.8%). Most women with anxiety disorders who did want treatment (20.2%) were receiving treatment. The majority of participants with anxiety disorders had a history of mental health problems (64.6%).

Prevalence rates overall are consistent with previous research, lending validity to the findings. However, findings challenge the assumption that everyone with a psychological disorder wants treatment. These findings highlight the importance of relationship-based care, where individual needs and contextual barriers to treatment can be explored.

Anxiety in pregnancy and after giving birth (the perinatal period) is highly prevalent but under-recognised. Robust methods of assessing perinatal anxiety are essential for services to identify and treat women appropriately.

To determine which assessment measures are most psychometrically robust and effective at identifying women with perinatal anxiety (primary objective) and depression (secondary objective).

We conducted a prospective longitudinal cohort study of 2243 women who completed five measures of anxiety and depression (Generalized Anxiety Disorder scale (GAD) two- and seven-item versions; Whooley questions; Clinical Outcomes in Routine Evaluation (CORE-10); and Stirling Antenatal Anxiety Scale (SAAS)) during pregnancy (15 weeks, 22 weeks and 31 weeks) and after birth (6 weeks). To assess diagnostic accuracy a sample of 403 participants completed modules of the Mini-International Neuropsychiatric Interview (MINI).

The best diagnostic accuracy for anxiety was shown by the CORE-10 and SAAS. The best diagnostic accuracy for depression was shown by the CORE-10, SAAS and Whooley questions, although the SAAS had lower specificity. The same cut-off scores for each measure were optimal for identifying anxiety or depression (SAAS ≥9; CORE-10 ≥9; Whooley ≥1). All measures were psychometrically robust, with good internal consistency, convergent validity and unidimensional factor structure.

This study identified robust and effective methods of assessing perinatal anxiety and depression. We recommend using the CORE-10 or SAAS to assess perinatal anxiety and the CORE-10 or Whooley questions to assess depression. The GAD-2 and GAD-7 did not perform as well as other measures and optimal cut-offs were lower than currently recommended.