In a pregnant woman diagnosed with gestational diabetes mellitus, when are repeat 75‑g oral glucose tolerance tests indicated?

Follow-Up OGTT for Gestational Diabetes

Women diagnosed with gestational diabetes mellitus should undergo a 75-g oral glucose tolerance test at 4-12 weeks postpartum to screen for persistent diabetes or prediabetes, and then continue lifelong screening at least every 3 years. 1

Postpartum Testing (Primary Indication for Repeat OGTT)

The most critical repeat OGTT occurs in the postpartum period:

• All women with GDM must be reevaluated at 4-12 weeks postpartum using a 75-g OGTT with clinically appropriate non-pregnancy diagnostic criteria to detect persistent diabetes or prediabetes 1, 2, 3, 4, 5
• This postpartum testing is mandatory because women with GDM have a 3.4-fold increased risk of developing type 2 diabetes later in life 2
• Use standard WHO diagnostic criteria for the postpartum OGTT (not pregnancy-specific thresholds) 3, 4, 5

Long-Term Surveillance

Beyond the immediate postpartum period, ongoing monitoring is essential:

• Lifelong screening for diabetes or prediabetes should occur at least every 3 years in women with normal postpartum glucose tolerance 1, 2
• Some guidelines recommend assessment every 2-3 years using fasting glucose, random glucose, HbA1c, or optimally a repeat OGTT 4, 5
• Women found to have prediabetes should receive intensive lifestyle interventions or metformin to prevent progression to diabetes 1

Repeat OGTT During Pregnancy (Third Trimester)

While not routinely recommended, repeat OGTT during pregnancy may be indicated in specific circumstances:

• Consider repeating the OGTT in the third trimester if clinical signs or symptoms suggestive of GDM develop after an initial negative screening at 24-28 weeks 6
• Research shows that approximately 23.5% of women who undergo a second OGTT in the third trimester after initial negative results will be diagnosed with GDM 6
• Specific indications for third-trimester repeat testing include:
  • Evidence of excessive fetal growth (macrosomia) on ultrasound 6
  • History of prior GDM (odds ratio 2.6 for positive second OGTT) 6
  • Higher glucose values on the index OGTT, even if below diagnostic thresholds (fasting ≥4.8 mmol/L or 2-hour ≥6.5 mmol/L) 6
  • New onset glucosuria or other clinical symptoms of diabetes 3, 4, 5

Important Clinical Considerations

Common pitfalls to avoid:

• Do not assume that women with GDM will automatically return to normal glucose tolerance postpartum—active follow-up and testing are required 1
• Do not rely solely on fasting glucose or HbA1c for postpartum screening; the 75-g OGTT is the recommended test as it can detect impaired glucose tolerance that other tests might miss 1, 4
• Do not delay postpartum testing beyond 12 weeks, as this is a critical window for reclassifying glucose tolerance status 1, 4, 5

Special populations:

• In women with a history of bariatric surgery, OGTT is not recommended due to risk of postprandial hypoglycemia; use alternative glucose assessment methods 4, 5