At what point during pregnancy should a woman suspected of having a condition be tested?

Gestational Diabetes Screening During Pregnancy

Women suspected of having gestational diabetes should be screened at their first prenatal visit if they have high-risk factors, and all other pregnant women should be screened between 24-28 weeks of gestation. 1, 2

Screening Timeline

First Prenatal Visit Screening

Women with high-risk factors should be tested for undiagnosed diabetes at their first prenatal visit:

• Marked obesity
• Personal history of gestational diabetes
• Strong family history of diabetes
• Previous delivery of macrosomic infant (>4.05 kg/9 lb)
• Glycosuria
• Polycystic ovary syndrome (PCOS)
• Member of high-risk ethnic group (Hispanic, American Indian, Asian, African-American)
• History of abnormal glucose tolerance

1, 2

24-28 Weeks Gestation Screening

All pregnant women not previously known to have diabetes and not meeting low-risk criteria should be screened for gestational diabetes at 24-28 weeks of gestation. 2, 1, 2

Women who were screened early in pregnancy due to high-risk factors and had negative results should be rescreened at 24-28 weeks. 2

Screening Methods

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

Two-Step Approach

1. Initial screening with 50-g glucose challenge test (GCT), non-fasting

   • Positive threshold: ≥140 mg/dL (80% sensitivity) or ≥130 mg/dL (90% sensitivity)
   • Measure plasma glucose 1 hour after glucose load

2. If positive, perform diagnostic 100-g oral glucose tolerance test (OGTT) on a separate day

   • Must be performed after overnight fast of at least 8 hours
   • GDM diagnosed when at least two values meet or exceed:
     • Fasting: ≥95 mg/dL
     • 1-hour: ≥180 mg/dL
     • 2-hour: ≥155 mg/dL
     • 3-hour: ≥140 mg/dL

One-Step Approach

• Perform diagnostic 75-g OGTT in all women at 24-28 weeks
• GDM diagnosed when any one value meets or exceeds:
  • Fasting: ≥92 mg/dL
  • 1-hour: ≥180 mg/dL
  • 2-hour: ≥153 mg/dL

2, 1

Low-Risk Women (No Screening Required)

Women with ALL of the following characteristics are considered low-risk and do not require GDM screening:

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

2, 1

Clinical Considerations and Pitfalls

Common Pitfalls

1. Missing early screening in high-risk women - Delays diagnosis and treatment, potentially leading to adverse maternal and fetal outcomes
2. Assuming normal early screening eliminates need for 24-28 week testing - Women with negative early screening still need testing at 24-28 weeks
3. Improper test preparation - Inadequate fasting or carbohydrate intake can affect OGTT results
4. Overlooking postpartum screening - Women with GDM should be screened 6-12 weeks postpartum for persistent diabetes

Benefits of Screening

• Reduces risk of preeclampsia, macrosomia, and shoulder dystocia
• Allows for timely intervention to improve maternal and fetal outcomes
• Identifies women at risk for future development of type 2 diabetes

2, 1

Potential Harms

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

2

Postpartum Follow-up

All women with GDM should be screened for persistent diabetes at 6-12 weeks postpartum using the 75-g OGTT, and should receive subsequent screening for the development of diabetes at least every 3 years. 2, 1

Women with GDM have a 15-60% risk of developing type 2 diabetes within 5-15 years of delivery. 2

By following these evidence-based screening protocols, healthcare providers can identify and manage gestational diabetes to reduce maternal and fetal complications, including preeclampsia, fetal macrosomia, shoulder dystocia, and neonatal hypoglycemia.