At what Body Mass Index (BMI) should a pregnant woman be screened for diabetes during her first prenatal visit at week 12 or 14?

BMI Threshold for Early Diabetes Screening in Pregnancy

Screen pregnant women with BMI ≥30 kg/m² for diabetes at their first prenatal visit (12-14 weeks). The answer is A. 30.

Screening Recommendation

• Women with BMI ≥30 kg/m² should undergo diabetes screening at the first prenatal visit (12-14 weeks) according to the American College of Obstetricians and Gynecologists, American College of Physicians, and American Diabetes Association. 1, 2

• This early screening aims to detect pre-existing undiagnosed type 2 diabetes that was present before pregnancy, not just gestational diabetes which typically develops later in pregnancy. 1

• If the initial screening at 12-14 weeks is negative, these women must be rescreened at 24-28 weeks of gestation, as gestational diabetes may still develop during the standard screening window. 1, 2

Rationale for BMI ≥30 kg/m² Threshold

• The BMI ≥30 kg/m² cutoff represents a significantly elevated risk for both pre-existing diabetes and gestational diabetes, with a 4.14 times higher risk compared to women with normal BMI. 1

• This recommendation carries a high strength of evidence rating from multiple guideline societies including ACOG, ADA, and ACP. 1

Additional High-Risk Factors

Beyond BMI ≥30 kg/m², other factors that warrant early screening at 12-14 weeks include: 2

• Previous history of gestational diabetes
• Family history of diabetes in first-degree relatives
• High-risk ethnicity (Hispanic, Native American, South or East Asian, African American, Pacific Islander)
• History of delivering a macrosomic baby (>4.05 kg or 9 lb)
• Polycystic ovary syndrome (PCOS)
• Glucosuria

Important Clinical Caveat

• Recent randomized controlled trial data (2024) demonstrates that early screening in obese women does not improve perinatal outcomes compared to routine screening at 24-28 weeks. 3, 4

• Despite this lack of outcome benefit, the guideline recommendation remains unchanged because early screening identifies pre-existing diabetes that requires immediate management, which is clinically distinct from gestational diabetes. 1

• The composite adverse perinatal outcome (macrosomia, cesarean delivery, hypertensive disorders, shoulder dystocia, neonatal hyperbilirubinemia, neonatal hypoglycemia) was not reduced by early screening in the largest RCT to date. 4

Common Pitfall to Avoid

• Failing to rescreen at 24-28 weeks after a negative early screening test is a critical error that results in missed diagnoses of gestational diabetes, which develops later in pregnancy even when early screening is normal. 1, 2