What are the guidelines for gestational diabetes screening and management?

Gestational Diabetes Screening Guidelines

All pregnant women without pre-existing diabetes should be screened for gestational diabetes mellitus (GDM) at 24-28 weeks of gestation to reduce maternal and fetal complications including preeclampsia, macrosomia, and shoulder dystocia. 1

Risk Assessment

High-Risk Women (Screen Early)

• Marked obesity
• Personal history of GDM
• Strong family history of diabetes
• Previous delivery of macrosomic infant (>4500g)
• Glycosuria
• Polycystic ovary syndrome (PCOS)
• High-risk ethnic groups (Hispanic, Native American, South/East Asian, African American, Pacific Islander) 1, 2

Low-Risk Women (May Not Require Screening)

• Age <25 years
• Normal pre-pregnancy weight (BMI ≤25 kg/m²)
• No family history of diabetes in first-degree relatives
• No history of glucose intolerance or adverse pregnancy outcomes related to GDM 1, 2

Screening Protocol

Timing

• High-risk women: At first prenatal visit AND again at 24-28 weeks if initial results negative 2
• Average-risk women: 24-28 weeks gestation 1

Screening Methods

Two approaches are commonly used:

1. Two-Step Approach (Most Common in US)

• Initial screening: 50g glucose challenge test (GCT), non-fasting
• Positive threshold: ≥140 mg/dL (7.77 mmol/L) or alternatively ≥130 mg/dL (7.21 mmol/L)
• If positive, proceed to diagnostic 100g oral glucose tolerance test (OGTT)
• GDM diagnosis: Two or more abnormal values on OGTT:
  • Fasting: ≥95 mg/dL
  • 1-hour: ≥180 mg/dL
  • 2-hour: ≥155 mg/dL
  • 3-hour: ≥140 mg/dL 1, 2

2. One-Step Approach

• 75g OGTT after fasting
• GDM diagnosis: One or more abnormal values:
  • Fasting: ≥92 mg/dL
  • 1-hour: ≥180 mg/dL
  • 2-hour: ≥153 mg/dL 1, 2

Management of GDM

Initial Treatment

• Moderate physical activity
• Dietary modifications
• Support from diabetes educators and nutritionists
• Blood glucose self-monitoring 1

Additional Treatment if Glucose Not Controlled

• Insulin therapy (first choice)
• Oral hypoglycemic agents may be considered
• Increased surveillance in prenatal care
• Potential changes in delivery management 1

Glucose Targets

• Fasting: <95 mg/dL
• 1-hour postprandial: <140 mg/dL 3

Postpartum Follow-Up

• All women with GDM should be screened for persistent diabetes at 6-12 weeks postpartum
• Subsequent screening every 2-3 years even if initial postpartum screening is normal 2, 3

Important Considerations and Pitfalls

Benefits of Screening

• Reduces risk for preeclampsia, macrosomia, and shoulder dystocia
• Early identification allows for timely intervention 1

Potential Harms

• Short-term anxiety with positive screening results
• Increased number of prenatal visits
• Possible unnecessary interventions with false positives 1

Common Pitfalls

• Missing high-risk women who need early screening
• Assuming normal early screening eliminates need for 24-28 week testing in high-risk women
• Overlooking postpartum screening for diabetes development 2

Evidence Quality

The USPSTF concludes with moderate certainty that there is a moderate net benefit to screening for GDM after 24 weeks of gestation. However, evidence for screening before 24 weeks remains insufficient, even in high-risk populations 1.

The 140 mg/dL threshold for the GCT offers high sensitivity with better specificity than the 130 mg/dL threshold 4, making it the preferred cutoff value for most screening protocols.