Psychometric validation of the Internalised Stigma Scale for Gestational Diabetes Mellitus (ISS-GDM): a cross-sectional study

OBJECTIVES: To develop and validate the Internalised Stigma Scale for Gestational Diabetes Mellitus (ISS-GDM), a questionnaire measuring self-reported internalised stigma among women with prior gestational diabetes mellitus (GDM). We hypothesised that internalised GDM stigma could be reliably and validly assessed through a short psychometric instrument. DESIGN: Cross-sectional validation study. SETTING: Follow-up data from the Danish, multicentre Face-it trial for women with prior GDM and their families. PARTICIPANTS: In total, 248 women completed the ISS-GDM approximately 1 year after their GDM affected pregnancy. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was psychometric properties of the ISS-GDM, assessed using Cronbach's alpha, confirmatory factor analysis (CFA) and Rasch analysis (RA). Secondary outcomes included identification of item anomalies (local response dependence, differential item functioning). RESULTS: A large proportion of respondents endorsed statements reflecting self-disappointment, self-blame and an altered self-perception. Less endorsed statements included feeling inferior to other mothers or guilt towards family members due to GDM. The ISS-GDM demonstrated satisfactory psychometric properties. CFA indicated that item 2 assessing self-perceived capabilities as a mother did not load onto the main factor, while CFA and RA identified local response dependence and differential item functioning by body mass index. After adjustments, a two-factor solution supported calculating a sum score of items 1 and 3-11, with item 2 retained as a stand-alone indicator of perceived parenting capabilities. The 10-item scale demonstrated acceptable reliability (Cronbach's alpha=0.78). CONCLUSIONS: The ISS-GDM is a reliable and valid tool for assessing internalised stigma among women with prior GDM. Our findings further suggest that a substantial proportion of women with prior GDM experience self-blame and an altered self-perception due to their diagnosis. The ISS-GDM scale enables research into its prevalence, severity and consequences.