Increased physical activity can also improve metabolic control and reduce GDM risk in pregnant women. As maternal insulin resistance is integral to many complications of obese pregnancy the dietary intervention focuses on lowering the dietary glycaemic index (GI), previously shown to improve pregnancy outcome in women with gestational diabetes (GDM). We have developed a theoretically based behavioural group intervention (diet and physical activity) for obese pregnant women with the primary aim of improving maternal glucose homeostasis. Limitations of the existing evidence include poor study design, small sample size, absence of a theoretical basis and, importantly, no a priori demonstration of the feasibility of the intervention in regard to changing the specific behaviours targeted. Recent meta-analyses of relevant studies in obese women show modest restriction of GWG without robust evidence for improved clinical outcome. The majority of attempts to develop interventions have hitherto focused on limiting gestational weight gain (GWG) according to the USA Institute of Medicine (IOM) recommendations. Pregnant obese women have a heightened risk of adverse pregnancy outcomes, but at present there is no evidence-based intervention that can be introduced into clinical practice to improve pregnancy outcome in obese women. Obesity is prevalent in women of reproductive age in both high and low-to-middle income countries.