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Introduction: The Edinburgh Postnatal Depression Scale (EPDS) is the most widely used instrument in perinatal clinical practice and research based on a belief that somatic symptoms during the perinatal period impact on depression measurement validity and reliability. The Montgomery Åsberg Depression Rating Scale – Self report (MADRS-S) may have better psychometric performance as a screening and outcome instrument for depression.

Methods: Self-referred pregnant women were screened (n = 650), diagnostically assessed (n = 390), treated with internet-based cognitive behavior therapy for depression (n = 270) and followed-up diagnostically (n = 169). EPDS and MADRS-S were assessed at screening and after treatment. Item level data from all patients were used in a series of psychometric tests including confirmatory factor analysis (CFA) and item response-theory tests (IRT).

Results: Both scales showed adequate reliability. Using depression as a unidimensional latent trait in CFA, MADRS-S fitted data better than EPDS. IRT revealed that the somatic items in MADRS-S contributed less than average rather than inflating the totals. For more depressed respondents, the EPDS scores' validity decreased compared to MADRS-S.

Conclusions: MADRS-S and EPDS are reliable tools for assessing depressive symptoms in pregnant patients, but MADRS-S outperforms EPDS on several key psychometric indicators. Contrary to common belief, somatic items seem not to inflate scores, and MADRS-S retains better precision at higher symptom levels. These findings support the use of standard depression measures, such as the MADRS-S, in pregnant populations. Doing so may improve detection and treatment by integrating antenatal depression into general psychiatric care and research rather than isolating it within perinatal-specific frameworks.