Because GDM often presents without obvious symptoms, universal screening is a standard of care in modern obstetrics. The screening typically occurs between 24 and 28 weeks of gestation, although high-risk patients (those with obesity or a history of GDM) are often screened during the first trimester.

The diagnostic process generally follows a one-step or two-step approach:

• The Two-Step Approach: Patients first undergo a 50-gram Glucose Challenge Test (GCT). If blood sugar exceeds a certain threshold (usually 130–140 mg/dL) after one hour, they move to the second step: a 100-gram, 3-hour Oral Glucose Tolerance Test (OGTT).

• The One-Step Approach: Recommended by the International Association of Diabetes and Pregnancy Study Groups (IADPSG), this involves a single 75-gram, 2-hour OGTT.

Diagnosis is confirmed if fasting or post-challenge glucose levels meet or exceed established thresholds. Early and accurate diagnosis is critical, as it allows for immediate lifestyle or pharmacological intervention to prevent fetal overgrowth.