Gestational Diabetes Mellitus: Screening and Management

SUMMARY:

Gestational diabetes mellitus (GDM) has become increasingly prevalent worldwide.  Class A1GDM refers to diet-controlled GDM. Class A2GDM refers to the clinical scenario where medications are required. The following synopsis highlights key practice points from various professional organizations. 

• Screening for GDM – One or Two Step?
• Who Should be Screened Early?
• Screening for Diabetes and Pre-Diabetes in The Postpartum Period
• What Are Glucose Target Levels?
• Diet and Exercise
• Pharmacologic Treatment
• Fetal Monitoring
• When to Deliver?

Screening for GDM – First or Second Trimester?

• ACOG supports the ‘2 step’ approach (24 to 28 week 1 hour venous glucose measurement following 50g oral glucose solution), followed by a 100g 3 hour oral glucose tolerance test (OGTT) if positive
  • Note: Diagnosis of GDM is based on 2 abnormal values on the 3 hour OGTT
    • ACOG recommends that currently there is insufficient evidence to diagnose GDM based on only one abnormal value
    • Patients with only one elevated value may require additional surveillance
• ACOG does not recommend routine screening for GDM <24 weeks 
• The USPSTF
  • Recommends screening for gestational diabetes in asymptomatic pregnant persons at ≥24 weeks of gestation or after (B recommendation)
  • Current evidence is insufficient to assess the balance of benefits and harms of screening for gestational diabetes in asymptomatic pregnant persons <24 weeks of gestation (I statement)
• ACOG and ADA prefer use of Carpenter and  Coustan vs national Diabetes Data Group (NDDG) criteria because the higher NDDG thresholds may result in missed opportunities to treat patients would would benefit from GDM diagnosis
  • Fasting blood sugar: <95 mg/dL (5.3 mmol/L)
  • 1 hour blood sugar: <180 mg/dL (10.0 mmol/L)
  • 2 hour blood sugar: <155 mg/dL (8.6 mmol/L)
  • 3 hour blood sugar: <140 mg/dL (7.8 mmol/L) 

Who Should be Screened Early?

The ACOG update is based on ADA criteria | Consider early screening in pregnancy if patient is overweight with BMI of ≥25 kg/m3 (23 in Asian Americans), and one or more of the following

• Physical inactivity
• Family history of diabetes – 1st degree relative (parent or sibling)
• Black, Hispanic, Native American, Asian American, or Pacific Islander
• Previous pregnancy history of
  • GDM
  • Macrosomia (≥ 4000 g)
• Hypertension (140/90 mm Hg or being treated for hypertension) 
• HDL cholesterol ≤ 35 mg/dl (0.90 mmol/L)
• Fasting triglyceride ≥ 250 mg/dL (2.82 mmol/L)
• PCOS
• Conditions associated with insulin resistance (e.g., acanthosis nigricans, morbid obesity)
• Hgb A1C ≥ 5.7%, impaired glucose tolerance or impaired fasting glucose | If A1C>6.5%, diagnosis of pregestational diabetes is met and GCT/GTT not needed
• Cardiovascular disease
• HIV
• 35 years or older 
• Other factors suggestive of increased risk for pregestational diabetes

Note: The ADA (2025) uses 130/80 as the BP threshold for hypertension diagnosis 

GDM Testing in Early Pregnancy 

• Best test method is unclear 
• Nonpregnant approach ‘could’ be use 
  • Fasting blood glucose followed by a 75-g glucose load and a 2-hour plasma glucose measurement
• 2 step approach (see above) is commonly used
  • Start with 50 g screening test with follow-up if initial screening test is positive  

Note: In case of a negative result in early pregnancy, GDM screening 24 to 28 weeks is still recommended | If initial 50 g screening test is positive but follow-up is negative, move on to follow-up test between 24 and 28 weeks as repeating the 50 g screening test is not necessary 

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