The screening, diagnosis, and classification of diabetes mellitus in pregnancy are critical to ensure optimal maternal and fetal health outcomes. Pregnant women are routinely screened for gestational diabetes mellitus (GDM) between 24-28 weeks of gestation using glucose challenge tests followed by diagnostic oral glucose tolerance tests (OGTT) if initial screening is positive. Pre-existing diabetes, including type 1 or type 2 diabetes diagnosed before pregnancy, requires early identification and management to minimize risks such as congenital anomalies and macrosomia. Proper classification based on glucose levels helps guide appropriate management strategies, including diet modification, glucose monitoring, insulin therapy, and close prenatal care coordination between obstetricians, endocrinologists, and other healthcare providers. Regular monitoring throughout pregnancy and postpartum is crucial to mitigate complications and ensure the best possible outcomes for both mother and baby.