What are the American College of Obstetricians and Gynecologists (ACOG) guidelines for screening and managing gestational diabetes in pregnant patients with a Body Mass Index (BMI) of 30 or higher?

ACOG Guidelines for Gestational Diabetes Screening in Pregnant Patients with BMI ≥30

Pregnant women with BMI ≥30 kg/m² should undergo glucose screening at their first prenatal visit (12-14 weeks gestation) to detect pre-existing undiagnosed type 2 diabetes, and if negative, must be rescreened at 24-28 weeks gestation using standard GDM screening protocols. 1, 2

Early Screening Protocol (First Prenatal Visit)

For women with BMI ≥30 kg/m²:

• Screen at 12-14 weeks gestation (or as soon as feasible after pregnancy confirmation) using standard diagnostic criteria for diabetes 3, 1, 2
• This early screening identifies pre-existing type 2 diabetes that was undiagnosed before pregnancy, not just gestational diabetes 1
• If fasting plasma glucose ≥126 mg/dL or random glucose ≥200 mg/dL with symptoms, diagnose as overt diabetes complicating pregnancy 1
• Critical caveat: Recent high-quality RCT evidence (2024) demonstrates that early screening in obese women does not improve perinatal outcomes compared to routine screening, though guideline recommendations remain unchanged 4

Standard Screening at 24-28 Weeks

All women with BMI ≥30 kg/m² who tested negative at first visit must be rescreened at 24-28 weeks gestation 1, 2

Two-Step Approach (ACOG-Endorsed Method):

• Step 1: 50g glucose challenge test (non-fasting) 3, 2, 5
• If plasma glucose ≥130-140 mg/dL at 1 hour, proceed to Step 2 3, 2
• Step 2: 100g oral glucose tolerance test (fasting) 2, 5
• Diagnosis requires ≥2 abnormal values: 2, 5
  • Fasting ≥95 mg/dL
  • 1-hour ≥180 mg/dL
  • 2-hour ≥155 mg/dL
  • 3-hour ≥140 mg/dL

One-Step Approach (Alternative):

• 75g OGTT with fasting, 1-hour, and 2-hour measurements 3, 2
• Diagnosis requires only 1 abnormal value: 3, 2
  • Fasting ≥92 mg/dL
  • 1-hour ≥180 mg/dL
  • 2-hour ≥153 mg/dL

Evidence Quality and Clinical Context

The recommendation for early screening in obese women represents high-strength guideline consensus from ACOG, ADA, and ACP 1. However, the most recent and highest quality evidence (2024 multicenter RCT) found that early GDM screening in patients with BMI ≥30 kg/m² does not prevent adverse perinatal outcomes 4. This study showed no reduction in the composite outcome of macrosomia, primary cesarean delivery, hypertensive disorders, shoulder dystocia, neonatal hyperbilirubinemia, or neonatal hypoglycemia 4.

Important finding: Patients with ≥3 additional risk factors may actually have worse outcomes with early screening 4. Despite this evidence, current ACOG guidelines maintain the recommendation for early screening, likely because it identifies pre-existing diabetes rather than preventing GDM-related complications 1.

Additional Risk Factors Warranting Early Screening

Beyond BMI ≥30 kg/m², these factors also indicate need for first-visit screening 3, 1:

• History of previous GDM (4.14× increased risk) 1
• First-degree relative with diabetes 1
• High-risk ethnicity (Hispanic, Native American, South/East Asian, African American, Pacific Islander) 3, 1
• History of delivering macrosomic baby (>4.05 kg) 1
• History of polycystic ovary syndrome 1

Critical Pitfall to Avoid

Failing to rescreen at 24-28 weeks after negative early screening is a major error 1. GDM typically develops in the second/third trimester due to increasing insulin resistance, so a negative early test does not exclude later development of GDM 1. Not repeating screening leads to delayed diagnosis and increased risk of maternal-fetal complications 1.

Postpartum Follow-Up

• Screen for persistent diabetes at 4-12 weeks postpartum using 75g OGTT 1, 2, 5
• Continue lifelong screening every 1-3 years thereafter 1, 2, 5
• Women with prediabetes should receive intensive lifestyle interventions or metformin 1, 2

Outcomes That Matter

The rationale for screening and treatment is reduction in serious perinatal complications. Treatment of GDM reduces macrosomia and shoulder dystocia with a number needed to treat of 34 3. The USPSTF found moderate net benefit for reducing preeclampsia, macrosomia, and shoulder dystocia collectively when screening after 24 weeks 3, 1. However, treatment does not reduce cesarean delivery rates or NICU admissions 3.