Measuring maternal mental health using the Dutch Four-Dimensional Symptom Questionnaire (4DSQ): Pregnancy-related item bias across the perinatal period.

Objective: the Four-Dimensional Symptom Questionnaire (4DSQ) measures four dimensions of common psychopathology: distress, depression, anxiety and somatization. The instrument is developed and validated for general practice. A previous validation study of the 4DSQ for midwifery practice indicated that pregnant women respond differently to the items of the 4DSQ. This phenomenon is called item bias. The present study is a followup validation study in which pregnant women were followed up until one year post partum, to assess pregnancy-related item bias.
Design: cohort study with repeated measurements.
Setting and Participants: the research group consisted of participants of the Mom@Work study, a study concerning mental health in a group of 574 working pregnant women and young mothers, recruited between 2004 and 2006. Measurements in the research group took place at 33 weeks of pregnancy and post partum at 7, 13, 25 and 52 weeks. The comparison group consisted of female general practice patients, matched for age (N=835).
Measurements and Findings: pregnancy-related item bias was assessed by two methods of differential item functioning (DIF) analysis: ordinal logistic regression (OLR) and the Mantel-Haenszel (MH) method. The impact of item bias on total scale scores was estimated by linear regression. Impact of item bias was found in the somatization-, distress- and anxiety scales of the 4DSQ across the perinatal period up until 13 weeks post partum. The depression scale remained free of item bias.
Key Conclusions and Implications for Practice: pregnant and postpartum women responded differently to the 4DSQ than the women in the comparison group up until 13 weeks post partum. Pregnancy-related item bias lead to overestimation of distress and underestimation of somatization and anxiety. The depression scale was free of bias. The 4DSQ is a valid tool for case-finding and assessment of psychological conditions in the perinatal period, provided cut-off points are adapted up until 13 weeks post partum. Validation of generic questionnaires is recommended before using them in the perinatal period.
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