Gestational diabetes mellitus (GDM) is a transient hyperglycemic condition identified during pregnancy in women without a history of chronic diabetes. Evidence indicates that GDM can lead to various adverse health outcomes, including preterm birth, progression to pre-diabetes, and type 2 diabetes after delivery in mothers. Notably, GDM is becoming increasingly prevalent among Asian pregnant women due to rising rates of overweight and obesity, as well as genetic susceptibility. Despite growing recognition of GDM, its treatment efficiency and efficacy remain poor, primarily due to its heterogeneity, which is underpinned by various pathophysiological mechanisms. Therefore, a better understanding of GDM heterogeneity can aid clinicians in providing more targeted treatment and follow-up strategies for GDM mothers. This study aims to define GDM phenotypes based on in vivo cardio-metabolic profiles and treatment response during pregnancy, utilizing advanced technologies such as continuous glucose profiling and untargeted metabolite profiling. In this proposed 3-year pregnancy cohort study, the investigators will recruit 800 overweight or obese Asian pregnant women in early pregnancy, without a history of diabetes, and follow them through to delivery. The goal of the study is to develop systematic antenatal and postnatal screening, treatment, and intervention guidelines for mothers with GDM.