Bariatric surgery is an effective and increasingly used treatment modality for severe obesity and its complications including diabetes mellitus. It is clearly more effective that intensive lifestyle interventions in achieving sustainable weight loss and is associated with >50% remission of known pre-existing diabetes. In addition to remission of diabetes, other comorbid conditions including hyperlipidaemia, hypertension and obstructive sleep apnoea are improved after bariatric surgery.
Some of the improvement in glucose metabolism following bariatric surgery occurs very rapidly, before the time of major weight loss and may relate to marked caloric restriction, improved insulin secretion and variable improvements in peripheral insulin resistance and hepatic glucose production. The function of the incretin system (GLP1 and GIP) is also enhanced following bariatric surgery.
Conventional OGTT diagnosis of gestational diabetes mellitus (GDM) is rarely feasible or useful following malabsorptive bariatric surgery and its utility after gastric sleeve procedures is debated. Major issues include variable gastric emptying, poor tolerance of the OGTT solution and hypoglycaemia during the test. A variety of bodies have produced consensus recommendations regarding diagnosis of GDM following bariatric surgery, often promoting use of HbA1c and home glucose monitoring (or continuous glucose monitoring if available) but none has a firm evidence based.
Whilst there is a clear consensus in favour of treating “diabetes level” hyperglycemia in pregnant women with previous bariatric surgery, the value of treating GDM is less clear and the potential reduction in excess fetal growth must be balanced against the risk of growth restriction.
Many aspects of the detection and treatment of hyperglycaemia during pregnancy in women with previous bariatric surgery remain contentious and further research should be a major priority.