Comparison of screening accuracy of the Patient Health Questionnaire-2 using two case-identification methods during pregnancy and postpartum

Background: Variation exists regarding perinatal depression screening. A two-step screening method has been recommended. According to a maternity-focused core outcome set developed by the International Consortium for Health Outcomes Measurement, women who score 3 or more on the PHQ-2 then complete the Edinburgh Postnatal Depression Scale (EPDS). Limited evidence exists regarding the screening accuracy of the PHQ-2 in childbearing women. An alternative case-identification method may be more sensitive for perinatal women. We aimed to [1] evaluate the screening accuracy of the PHQ-2 during the perinatal period using two case-identification methods, and [2] measure the variability of accuracy over four time-points during pregnancy and postpartum. Methods: A prospective, longitudinal cohort study was conducted with 309 consecutive women who completed the PHQ-2 and EPDS during pregnancy (booking, 36-weeks) and postpartum (6-, 26-weeks). EPDS was the reference standard using cut-off scores for 'at least probable minor depression' during pregnancy (≥ 13) and postpartum (≥ 10) and for 'probable major depression' during pregnancy (≥ 15) and postpartum (≥ 13). PHQ-2 was analysed using two methods: [1] scored (cut-points ≥ 2 and ≥ 3), [2] dichotomous yes/no (positive response to either question) against EPDS cut-points for at least probable minor and probable major depression. Receiver operating characteristic analyses determined accuracy. Results: Probable major depression: Over four timepoints PHQ-2 ≥ 3 revealed lowest sensitivity (36-79%) but highest specificity (94-98%). An alternative case-identification method revealed high sensitivity (93-100%), but lowest specificity (58-71%). Minor depression: PHQ-2 ≥ 3 revealed the lowest sensitivity (19-50%) but highest specificity (95-98%). An alternative case-identification method revealed the highest sensitivity (81-100%) and moderate specificity (60-74%). Conclusions: Recommended method of case-identification (PHQ-2 ≥ 3) missed an unacceptable number of women at-risk of depression. As a clinical decision-making tool, an alternative, dichotomous method maximized case-identification and is recommended. Further, the literature identified inconsistent reporting of the PHQ-2 and the alternative case-identification method hindering the ability to synthesise data. The future use and reporting of consistent question wording and response format will improve outcome reporting and synthesis. Further research in larger and diverse maternity populations is recommended.