Glutamic acid decarboxylase autoantibody-positivity post-partum is associated with impaired β-cell function in women with gestational diabetes mellitus

AimsTo investigate whether the presence of glutamic acid decarboxylase (GAD) autoantibodies post-partum in women with prior gestational diabetes mellitus was associated with changes in metabolic characteristics, including -cell function and insulin sensitivity. MethodsDuring 1997-2010, 407 women with gestational diabetes mellitus were offered a 3-month post-partum follow-up including anthropometrics, serum lipid profile, HbA(1c) and GAD autoantibodies, as well as a 2-h oral glucose tolerance test (OGTT) with blood glucose, serum insulin and C-peptide at 0, 30 and 120min. Indices of insulin sensitivity and insulin secretion were estimated to assess insulin secretion adjusted for insulin sensitivity, disposition index (DI). ResultsTwenty-two (5.4%) women were positive for GAD autoantibodies (GAD+ve) and the remainder (94.6%) were negative for GAD autoantibodies (GAD-ve). The two groups had similar age and prevalence of diabetes mellitus. Women who were GAD+ve had significantly higher 2-h OGTT glucose concentrations during their index-pregnancy (10.5 vs. 9.8mmol/l, P=0.001), higher fasting glucose (5.2 vs. 5.0mmol/l, P=0.02) and higher 2-h glucose (7.8 vs. 7.1mmol/l, P=0.05) post-partum. Fasting levels of C-peptide and insulin were lower in GAD+ve women compared with GAD-ve women (520 vs. 761pmol/l, P=0.02 and 33 vs. 53pmol/l, P=0.05) Indices of insulin sensitivity were similar in GAD+ve and GAD-ve women, whereas all estimates of DI were significantly reduced in GAD+ve women. ConclusionGAD+ve women had higher glucose levels and impaired insulin secretion adjusted for insulin sensitivity (DI) compared with GAD-ve women. The combination of OGTT and GAD autoantibodies post-partum identify women with impaired -cell function. These women should be followed with special focus on development of Type1 diabetes.