When should gestational diabetes be suspected in pregnant women?

When to Suspect Gestational Diabetes Mellitus (GDM)

Gestational diabetes should be suspected in all pregnant women, with universal screening recommended at 24-28 weeks of gestation, and immediate screening for those with high-risk factors at the first prenatal visit. 1

Risk Assessment at First Prenatal Visit

All pregnant women should undergo risk assessment for GDM at their first prenatal visit. This risk stratification determines the timing of screening:

High-Risk Women (Immediate Screening)

Women with clinical characteristics consistent with high risk should undergo glucose testing as soon as feasible after pregnancy confirmation 1:

• Severe obesity
• Personal history of GDM
• Previous delivery of large-for-gestational-age infant
• Presence of glycosuria
• Diagnosis of polycystic ovary syndrome (PCOS)
• Strong family history of type 2 diabetes
• Belonging to high-risk ethnic groups (Hispanic, Native American, South or East Asian, African American, Pacific Islander)

Average-Risk Women

• Should be tested at 24-28 weeks of gestation 1

Low-Risk Women (May Skip Screening)

Women meeting ALL of the following criteria may not require screening 1:

• Age younger than 25 years
• Normal pre-pregnancy weight (BMI ≤25 kg/m²)
• Member of ethnic group with low prevalence of diabetes
• No known diabetes in first-degree relatives
• No history of abnormal glucose tolerance
• No history of poor obstetrical outcomes

Warning Signs and Symptoms

While GDM is often asymptomatic, certain clinical presentations should raise suspicion:

• Excessive fetal growth (fundal height greater than expected for gestational age)
• Polyhydramnios
• Glycosuria on routine urinalysis
• Recurrent urinary tract infections
• Unexplained fetal loss

Screening Methods

Two approaches are commonly used for screening at 24-28 weeks 1:

Two-Step Approach

1. Initial screening with 50-g oral glucose challenge test (GCT) in non-fasting state
2. If screening threshold is met or exceeded (≥130-140 mg/dL), proceed to diagnostic 100-g OGTT

One-Step Approach

• Direct 75-g OGTT without prior screening
• May be preferred in clinics with high prevalence of GDM

Important Clinical Considerations

• If high-risk women test negative at initial screening, they should be retested between 24-28 weeks of gestation 1
• Post-partum follow-up: Women with GDM should be screened for diabetes 6-12 weeks postpartum 1
• Long-term monitoring: These women require lifelong monitoring due to increased risk of developing type 2 diabetes 1

Pitfalls to Avoid

• Relying solely on risk factors: Studies show that 12% of women with GDM have no identifiable risk factors 2
• Missing early GDM: Recent evidence suggests 30-70% of GDM cases can be diagnosed in early pregnancy (before 20 weeks) 3
• Overlooking borderline results: Women with borderline glucose tolerance but multiple risk factors may still be at high risk for adverse outcomes 4
• Delaying treatment: Early diagnosis and treatment improve both maternal and fetal outcomes 5

The USPSTF concludes that evidence for screening before 24 weeks is insufficient, but clinical judgment should be used for high-risk women 1. Given the increasing prevalence of diabetes and obesity, a lower threshold for suspicion is warranted in today's clinical practice.