Mothers with previous gestational diabetes mellitus (GDM) represent a population at higher risk of future Type 2 diabetes mellitus (T2DM), which is preventable through lifestyle modification. Yet, no formal prevention programs exist for this population. The postpartum period is a particularly vulnerable period for weight gain and unhealthy lifestyle in new mothers due to their competing demands of childcare and breastfeeding. This important time period may thus represent a 'window of opportunity' for women with previous GDM, whereby interventions to improve their lifestyle can be offered. Eligible women will be recruited during pregnancy from four hospitals and invited to participate in a home-based lifestyle intervention program starting from three to six months postpartum. This pilot study will investigate the feasibility and effectiveness of a physical activity and diet intervention. It will also explore the relationship between behaviour change and metabolic markers of T2DM in this high-risk population. Investigators hypothesize that the ADAPT-M program will be feasible and will be associated with an improvement in metabolic T2DM markers, as well as a high rate of satisfaction, adherence, and effectiveness.