How is gestational diabetes (GDM) resolved postpartum?

Postpartum Testing for Resolution of Gestational Diabetes

Women with gestational diabetes mellitus (GDM) should undergo a 75-gram oral glucose tolerance test (OGTT) at 4-12 weeks postpartum using non-pregnancy diagnostic criteria to determine if diabetes or prediabetes persists. 1

Why OGTT is Required (Not A1C)

The OGTT is specifically mandated over A1C testing in the early postpartum period for several physiological reasons:

• Increased red blood cell turnover during pregnancy artificially lowers A1C values, making them unreliable for diagnosis 1
• Blood loss at delivery further distorts A1C results, potentially masking persistent hyperglycemia 1
• The preceding 3-month glucose profile affects A1C, which may not reflect current postpartum glucose metabolism 1
• OGTT is more sensitive than A1C for detecting both prediabetes and diabetes in the postpartum period 1

Diagnostic Criteria for Postpartum OGTT

Use standard non-pregnancy diagnostic thresholds for the 75-gram OGTT 1:

• Diabetes diagnosis: Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L) OR 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) 1
• If both fasting and 2-hour values meet diabetes criteria, the diagnosis is confirmed with a single test 1
• If only one value is abnormal, repeat testing is required to confirm persistent abnormality 1
• Prediabetes: Impaired fasting glucose (100-125 mg/dL) or impaired glucose tolerance (2-hour value 140-199 mg/dL) 1

Expected Outcomes at Postpartum Testing

Research demonstrates variable rates of persistent glucose intolerance:

• Approximately 65-70% of women return to normal glucose tolerance 2
• 30-44% develop prediabetes (impaired fasting glucose, impaired glucose tolerance, or both) 3, 2
• 1.5-3% have overt diabetes at the initial postpartum screening 3, 2

Risk Factors for Persistent Postpartum Glucose Intolerance

Women at highest risk for persistent dysglycemia include those with:

• Family history of type 2 diabetes (OR 2.21) 4
• All three glucose values exceeding thresholds during pregnancy OGTT (OR 2.89) 4
• Ethnic minority background (OR 2.76) 3
• Higher HbA1c levels during pregnancy 3, 4
• Insulin treatment required during pregnancy 4
• Obesity (higher prepregnancy BMI) 3, 2
• Advanced maternal age 3, 2

Long-Term Surveillance After Initial Testing

If the 4-12 week postpartum OGTT is normal, lifelong screening is mandatory every 1-3 years due to the dramatically elevated lifetime diabetes risk 1:

• 50-60% lifetime risk of developing type 2 diabetes 1
• Risk increases linearly: 20% at 10 years, 30% at 20 years, 40% at 30 years, 50% at 40 years, 60% at 50 years 1
• 10-fold increased risk compared to women without GDM 1

For ongoing surveillance after the initial postpartum period, any of these tests are acceptable 1:

• Annual A1C testing
• Annual fasting plasma glucose
• Triennial 75-gram OGTT (using non-pregnant thresholds)

Management of Abnormal Postpartum Results

Women with prediabetes identified at postpartum testing should receive intensive lifestyle interventions and/or metformin to prevent progression to type 2 diabetes 1, 5

Common Pitfalls to Avoid

• Do not test immediately postpartum while hospitalized: This has reduced sensitivity for detecting glucose intolerance 1
• Do not use A1C for the 4-12 week postpartum screening: It will miss cases due to pregnancy-related physiological changes 1
• Do not assume resolution without testing: Nearly half of women will have persistent glucose intolerance 3, 2
• Anticipate poor follow-up rates: Approximately 30% of women fail to attend postpartum OGTT, particularly those with higher BMI, ethnic minority background, and smoking history 3

Preconception Counseling for Future Pregnancies

Women with a history of GDM should undergo preconception screening for diabetes before subsequent pregnancies using glucose or HbA1c testing, as they may develop type 2 diabetes between pregnancies 1