What are the ACOG criteria for interpreting the 2‑hour plasma glucose value on a postpartum oral glucose tolerance test in women with prior gestational diabetes?

Postpartum OGTT Criteria for Women with Prior GDM

Women with a history of gestational diabetes should be screened at 6-12 weeks postpartum using a 75-g oral glucose tolerance test (OGTT) with standard nonpregnancy diagnostic criteria, NOT pregnancy-specific thresholds.

Standard Nonpregnancy Diagnostic Criteria for the 2-Hour Value

The 2-hour plasma glucose value on the postpartum OGTT should be interpreted using these thresholds 1:

• Diabetes: 2-hour glucose ≥200 mg/dL (11.1 mmol/L)
• Impaired glucose tolerance (prediabetes): 2-hour glucose 140-199 mg/dL (7.8-11.0 mmol/L)
• Normal: 2-hour glucose <140 mg/dL (7.8 mmol/L)

Additionally, evaluate the fasting value:

• Diabetes: Fasting glucose ≥126 mg/dL (7.0 mmol/L)
• Impaired fasting glucose (prediabetes): Fasting glucose 100-125 mg/dL (5.6-6.9 mmol/L)
• Normal: Fasting glucose <100 mg/dL (5.6 mmol/L)

Critical Distinction: Pregnancy vs. Postpartum Criteria

Do not use the pregnancy GDM diagnostic thresholds postpartum. During pregnancy, the 2-hour cutoff for GDM diagnosis is 153 mg/dL (one-step) or 155 mg/dL (two-step Carpenter/Coustan), but these values are specifically calibrated for pregnancy physiology and adverse pregnancy outcomes 2.

Postpartum, you are screening for persistent diabetes or prediabetes using standard WHO/ADA nonpregnancy criteria because insulin resistance normalizes dramatically after delivery 1.

Confirmation Requirements

Important caveat: If diabetes is diagnosed based on a single abnormal OGTT value (either fasting ≥126 mg/dL OR 2-hour ≥200 mg/dL), the 2022 ADA criteria now require confirmation with a second abnormal test on a different day in the absence of unequivocal hyperglycemia 3. If both the fasting AND 2-hour values meet diabetes criteria on the same OGTT, diabetes is confirmed without repeat testing 3.

Timing Considerations

• Optimal timing: 6-12 weeks postpartum 2, 1, 4
• Avoid immediate postpartum testing (within 48 hours): Recent evidence shows inpatient testing yields falsely elevated rates of glucose intolerance and diabetes diagnoses, particularly on postpartum day 1 5
• Do not use A1C at the 6-12 week postpartum visit, as it may be artificially lowered by increased red blood cell turnover during pregnancy, blood loss at delivery, or the preceding glucose profile 1, 3

Long-Term Follow-Up Algorithm

After the initial postpartum OGTT 2, 3:

1. If normal: Repeat screening every 1-3 years using any standard test (A1C, fasting glucose, or OGTT)
2. If prediabetes diagnosed: Offer intensive lifestyle interventions or metformin to prevent progression to diabetes 2, 3
3. Before any future pregnancy: Screen again for diabetes to identify women who have progressed since the last pregnancy 3

The lifetime risk of developing type 2 diabetes after GDM is substantial—approximately 50-60% within 10-20 years—making this long-term surveillance critical 6, 3.