Psychometric validation of the Patient Health Questionnaire-9 for pregnant women: A comprehensive longitudinal study in China.

BACKGROUND

The Patient Health Questionnaire-9 (PHQ-9) is widely used for screening antenatal depression. However, evidence on its longitudinal psychometric properties in pregnant populations remains limited. This study aimed to evaluate the performance of the PHQ-9 among Chinese pregnant women using classical test theory (CTT) and item response theory.

METHODS

A total of 19,268 pregnant women were enrolled from Shenzhen Baoan Women's and Children's Hospital, China. The PHQ-9 was administered repeatedly across the first, second, and third trimesters. Psychometric properties of the PHQ-9 were investigated using CTT and Samejima's graded response model. Longitudinal measurement invariance was evaluated to examine the stability of the scale across trimesters.

RESULTS

The PHQ-9 showed satisfactory internal consistency (Cronbach's α = 0.79-0.80). A two-factor structure of somatic and cognitive-affective symptoms was consistently established. All items demonstrated acceptable discrimination, whereas items on somatic symptoms had lower difficulty thresholds in the first trimester, likely reflecting normative physiological changes. Item and test information functions demonstrated optimal precision for mild-to-moderate depressive severity, increasing slightly from early to late pregnancy. Longitudinal measurement invariance was partially supported, indicating that observed score changes may not fully reflect true changes in depressive severity.

CONCLUSIONS

The PHQ-9 is generally reliable and valid for assessing antenatal depression in Chinese women. However, its reliance on somatic items and partial longitudinal invariance suggests caution when interpreting raw score changes across trimesters. Complementary instruments may improve assessment, particularly in the first trimester. Future studies should incorporate clinical validation and cross-cultural samples to enhance the scale's applicability and longitudinal stability.