Gestational diabetes mellitus (GDM) affects one fifth of Singaporean pregnancies and can result in short and long term complications for mother and child. Mobile applications are effective in improving diabetes care and weight related behaviors through improved self-management. A multidisciplinary healthcare team from National University Hospital, Singapore has worked with Jana Care to develop the Habits-GDM smartphone app, a lifestyle coaching program specific for gestational diabetes. It consists of interactive lessons to provide patient education, diet, activity and weight tracking tools, messaging platform for coaching and motivating patients towards healthy behavior beneficial for gestational diabetes. It interfaces with the Aina device, a novel hardware sensor that plugs into any smartphone and can be used for glucose monitoring. This study aims to test the effectiveness of this app in preventing excessive weight gain in pregnancy among patients with gestational diabetes.