Trying to understand gestational diabetes.

Women with normal glucose tolerance pre-gravid and developing gestational diabetes in late gestation have subclinical metabolic dysfunction prior to conception compared with women with normal glucose tolerance. Because of the 60% decrease in insulin sensitivity with normal pregnancy, these women develop clinical hyperglycaemia/gestational diabetes in late gestation. The metabolic dysfunction includes impaired insulin response, decreased hepatic suppression of glucose production during insulin infusion and decreased insulin-stimulated glucose uptake in skeletal muscle, i.e. peripheral insulin resistance. The insulin resistance in normal glucose tolerance pregnancy is related to a decrease in the post-receptor insulin signalling cascade, specifically decreased insulin receptor substrate 1 tyrosine phosphorylation. In women with normal glucose tolerance this is reversed post-partum. In contrast, in gestational diabetes, in addition to the decrease in insulin receptor substrate 1 tyrosine phosphorylation, there is an additional decrease in tyrosine phosphorylation of the intracellular portion of the insulin receptor that is not related to the insulin receptor protein content. Post-partum women with gestational diabetes, who had retention of gestational weight gain, had no significant improvement in insulin sensitivity and increased inflammation expressed as increased plasma and skeletal muscle tumour necrosis factor alpha. The increased inflammation or meta-inflammation is a hallmark of obesity and during pregnancy develops in both white adipose tissue and placenta. Last gene array studies of placenta were associated with alterations in gene expression relating primarily to lipid in contrast to glucose metabolic pathways in gestational diabetes compared with Type 1 diabetes. Future studies are directed at decreasing inflammation prior to and during pregnancy using various lifestyle and nutritional interventions.