The Patient Health Questionnaire-9 among First-Trimester Pregnant Women in Japan: Factor Structure and Measurement and Structural Invariance between Nulliparas and Multiparas and across Perinatal Measurement Time Points

Background: Depression is frequently seen among pregnant women. The PHQ-9 is a diagnostic criteria-based screening instrument. Objective: The objective is to identify the factor structure of the Patient Health Questionnaire-9 (PHQ-9) and to confirm its measurement and structural invariance regarding parity and observation time, as well as to examine reliability by calculating omega indices in a population of pregnant Japanese women. Methods: The PHQ-9 was distributed to 382 pregnant women with a gestational age of 10 to 13 weeks who were attending antenatal clinics. Of these women, 129 were tested again with the PHQ-9 one week later. Results: Exploratory factor analyses (EFAs) of the PHQ-9 items were conducted using a halved sample. Confirmatory factor analyses (CFAs) among the other halved sample compared the single-, two-factor models derived from the EFAs, literature model and bifactor model. The bifactor model was significantly better in terms of goodness-of-fit indices: χ2/df = 1.030 (18), CFI = 0.999, RMSEA = 0.012. ECV suggested multidimensionality. Internal consistency was excellent: ω = 0.868, ω. Somatic factor = 0.756, ω. Non-somatic factor = 0.817. ωH = 0.795, ωHS. Somatic factor = 0.330, ωHS. Non-somatic factor = 0.032. The bifactor structure model showed configural, measurement, and structural invariances between primiparas and multiparas as well as at two observation occasions. Conclusion: The findings suggested that the PHQ-9 used among pregnant women was robust in its factor structure.