The Edinburgh Postnatal Depression Scale as a measure for antenatal dysphoria

Background: Data arising from the Edinburgh Postnatal Depression Scale (EPDS), used as screening tool for perinatal depression, have been analysed as unidimensional in some studies and multidimensional in others. This study evaluates the dimensionality and item properties of the EPDS. Methods: 920 women recruited in antenatal clinics from two government tertiary hospitals completed the English EPDS between 26 and 28 weeks of pregnancy. Classical test theory and factor analyses were used to evaluate dimensionality. Item response theory was used to investigate item functioning. Results: The EPDS was essentially unidimensional. It has a common factor, 'antenatal dysphoria' and 3 subdomains 'depressive' (items 7-10), 'anxiety' (items 3-5) and 'anhedonic symptoms' (items 1, 2). Item 8 (I have felt sad or miserable) (discrimination = 3.13. SE = 0.24), item 9 (I have been so unhappy that I have been crying) (discrimination = 2.39. SE = 0.17) and item 10 (The thought of harming myself has occurred to me) (discrimination = 2.27. SE = 0.21) best discriminated participants that had dysphoria. Item 1 (I have been able to laugh and see the funny side of things) (threshold 1 = 1.49, SE = 0.14), item 2 (I have looked forward with enjoyment to things) (threshold 1 = 1.21, SE = 0.11) and item 10 (The thought of harming myself has occurred to me) (threshold 1 = 1.19, SE = 0.21) indicated dysphoria severity. Conclusions: The EPDS measures antenatal dysphoria rather than just depression. It could be used to screen for antenatal depressive, anxiety and anhedonic symptoms. The items discriminate and grade dysphoria unequally. The findings may impact on scale use and interpretation.