PROBLEM: To determine if first trimester missed abortion decidua is characterized by an altered immune cell profile and/or a modified interleukin (I L)-10 and interferon (IFN)-gamma production pattern compared with decidua from elective termination. METHOD OF STUDY: Flow cytometry and immunohistochemistry techniques were used to determine the decidual immune cell phenotypic profile and production pattern of IL-10 and IFN-gamma in cases of elective termination (n = 14) and missed abortion (n = 12). RESULTS: Both groups had a similar proportion of CD56(+) CD16(-),CD56(+) CD16(+), CD19(+), CD3(+), CD4(+), CD8(+), alphabeta T cells and gammadelta T cells. The majority of alphabeta and gammadelta positive T cells in both groups coexpressed the natural killer (NK) cell marker CD56, but lacked cell surface expression of CD3. Diminished decidual IL-10 staining was noted in 7/10 missed abortion cases compared with none of the elective termination cases (n = 12) (P = 0.007). A uniform decidual IFN-gamma staining pattern was observed in both groups. CONCLUSION: Decreased IL-10 production coupled with a sustained IFN-gamma presence noted in missed abortion compared with elective termination cases suggest that these cytokines may be important determinants in pregnancy outcome. In contrast, differences in the proportion of immune cells between both groups may not be a critical factor in early pregnancy loss. In normal pregnancy, decidual alphabeta and gammadelta positive T cells with reduced CD3 on their cell surface may be intrinsically restricted in T-cell receptor (TCR)-mediated activation.