Screening for Gestational Diabetes

Risk Assessment and Timing

A 22-week pregnant woman with a family history of diabetes falls into the average-risk category for gestational diabetes mellitus (GDM) based on current guidelines from the American Diabetes Association 3, 4
High-risk criteria requiring immediate screening include marked obesity (BMI ≥30 kg/m²), personal history of previous GDM, glycosuria detected on urinalysis, and strong family history of diabetes (first-degree relative) 2, 5

At 24-28 weeks gestation, the American College of Obstetricians and Gynecologists recommends performing a 75g oral glucose tolerance test (OGTT) with fasting, 1-hour, and 2-hour glucose measurements as the preferred one-step approach 1, 5, 6
Diagnostic thresholds for the 75g OGTT are: fasting ≥92 mg/dL, 1-hour ≥180 mg/dL, and 2-hour ≥153 mg/dL, with any one value being diagnostic 5, 6
An alternative two-step approach involves a 50g glucose challenge test, followed by a 100g OGTT if the result is ≥140 mg/dL, with diagnostic thresholds of fasting ≥95 mg/dL, 1-hour ≥180 mg/dL, 2-hour ≥155 mg/dL, and 3-hour ≥140 mg/dL (requiring two or more values) 5, 7

The 75g OGTT has advantages including faster diagnosis, better patient tolerance, outcome-based criteria, simplicity, and international consensus 5, 6
A common pitfall to avoid is performing early screening in average-risk women, which may lead to overdiagnosis and unnecessary interventions 5, 7