One in five women in the UK is obese (BMI >30 kg/m2) at antenatal booking. Maternal obesity is associated with complications for the mother including increased risk of developing gestational diabetes, pre-eclampsia and need for caesarean section. For the offspring short term complications include risk of macrosomia and need for admission to the neonatal unit. It is now apparent that the effects of maternal obesity for the offspring extend beyond the neonatal period with increased risk of obesity in childhood, adolescence and adult life. In a recent record-linkage study we demonstrated that maternal obesity is associated with increased risk of premature mortality and hospital admissions for cardiovascular events in her adult offspring. Animal models suggest the adverse effects of maternal obesity on offspring outcomes are programmed in utero. To investigate underlying mechanisms we have been carrying out a casecontrol study of very severely obese pregnant women (BMI >40 kg/m2) vs. normal weight controls. We characterise maternal weight, body composition, and metabolic profiles through pregnancy and study infant growth and development at birth and 3 and 6 months. Placenta and cord blood are collected at birth. Our findings suggest early interventions to improve weight and diet in obese pregnant women are urgently needed. As lifestyle interventions in obese pregnancy are challenging, we have conducted a randomised controlled trial (EMPOWaR) in obese pregnant women using the insulin sensitiser metformin vs placebo. Outcomes for mother and child will be discussed.