Diagnosis and Management of Gestational Diabetes Mellitus

Diagnostic Approaches

The one-step approach uses a 75g oral glucose tolerance test (OGTT) with plasma glucose measurements taken when fasting and at 1 and 2 hours, performed between 24-28 weeks of gestation, and is preferred due to its ability to identify more cases of GDM and potentially reduce adverse pregnancy outcomes 1, 2
Diagnosis is made when any of the following plasma glucose values are met or exceeded: Fasting: 92 mg/dL, 1 hour: 180 mg/dL, 2 hour: 153 mg/dL 1, 2, 3
The American College of Obstetricians and Gynecologists notes that one elevated value can be used for diagnosis 1

Risk assessment for GDM should be undertaken at the first prenatal visit, and women with high-risk characteristics should undergo glucose testing as soon as feasible 4, 5
Women of average risk should have testing undertaken at 24-28 weeks of gestation 4, 3

Women with GDM should be screened for persistent diabetes at 4-12 weeks postpartum using a 75g OGTT 1, 3
Women with a history of GDM should have lifelong screening for diabetes or prediabetes at least every 3 years, and those found to have prediabetes should receive intensive lifestyle interventions or metformin to prevent diabetes 1, 3

Women diagnosed with GDM by the one-step approach have a 3.4-fold higher risk of developing prediabetes and type 2 diabetes later in life 5

The American Diabetes Association recommends that all women with a history of gestational diabetes undergo a 75‑g oral glucose tolerance test between 4 and 12 weeks after delivery, using standard non‑pregnancy diagnostic criteria to identify persistent diabetes or prediabetes. 6

After a normal postpartum OGTT, the same guideline advises lifelong diabetes screening at least every three years to detect later development of diabetes or prediabetes. 6
Women identified with prediabetes during follow‑up should be offered intensive lifestyle modification programs and, when appropriate, metformin therapy to reduce the risk of progression to overt diabetes. 6

The guideline emphasizes that clinicians must not assume spontaneous normalization of glucose tolerance after gestational diabetes; systematic postpartum testing and ongoing monitoring are required. 6
Reliance solely on fasting plasma glucose or HbA1c is discouraged for postpartum assessment; the 75‑g OGTT is preferred because it can uncover impaired glucose tolerance that single‑measure tests may miss. 6
Postpartum testing should be completed no later than 12 weeks after delivery, as this window is critical for accurately reclassifying a woman’s glucose‑metabolism status. 6