The invention involves assays, diagnostics, kits, and assay components for determining levels of glycated CD59 in the assessment of gestational diabetes mellitus and/or related disorders and/or conditions. Some kits comprise a capture antibody capable of associating with a capture epitope on CD59, wherein said capture epitope may lack lysine residue number 41 (K41 ). Kits may also comprise a detection antibody capable of associating with a detection epitope on CD59. Such detection epitopes may comprise glycated K41.