Overweight and obesity in the obstetric population can lead to many short- and long-term maternal and fetal complications. These were investigated in the Australasian Maternity Outcomes Surveillance Study (AMOSS). In this presentation, Dr Dekker Nitert presents the evidence on interventions used both prior to and during pregnancy to prevent complications in overweight and obese women. Pre-pregnancy interventions are aimed at achieving weight loss, while those during pregnancy are aimed at limiting weight gain. Dr Dekker Nitert also reviews the literature on the success of weight loss strategies including diet, exercise, bariatric surgery and pharmacotherapy. The barriers to pre-pregnancy weight loss are also discussed in this presentation. Finally, Dr Dekker Nitert highlights the role of probiotics in Gestational diabetes, a study looking at altering the composition of the gut microbiome in overweight and obese women to achieve weight loss.