What is the recommended approach for glucose screening and iron supplements in an asymptomatic pregnant woman with a normal pregnancy, no history of Gestational Diabetes Mellitus (GDM), and a Body Mass Index (BMI) of 24?

Glucose Screening and Iron Supplementation in Low-Risk Pregnancy

This asymptomatic pregnant woman with BMI 24 and no GDM history should receive standard glucose screening at 24-28 weeks gestation, not early screening, and should receive routine iron supplementation during the second and third trimesters. 1, 2

Glucose Screening Recommendation: Standard Timing at 24-28 Weeks

Early glucose screening (Option A) is NOT indicated for this patient. She does not meet any high-risk criteria that would warrant testing before 24 weeks. 1, 3, 4

Why Early Screening is Not Appropriate

This patient is explicitly low-risk based on the following characteristics:

• BMI of 24 kg/m² (normal weight, well below the BMI ≥30 kg/m² threshold for early screening) 3, 4
• No history of previous GDM (prior GDM confers 4.14 times higher risk and is a major indication for early testing) 3
• Asymptomatic with normal pregnancy 1

High-Risk Criteria Requiring Early Screening (Not Present in This Case)

Early screening at 12-14 weeks is reserved for women with:

• Severe obesity (BMI ≥30 kg/m²) 1, 3, 4
• Previous history of GDM 1, 3
• Strong family history of diabetes in first-degree relatives 1, 3
• Previous delivery of macrosomic infant (>4.05 kg) 3
• High-risk ethnicity (Hispanic, Native American, South/East Asian, African American, Pacific Islander) 3, 4
• Glycosuria or previous abnormal glucose metabolism 1

Standard Screening Protocol for This Patient

Universal screening at 24-28 weeks gestation is recommended for all pregnant women, including those without risk factors. 1, 3, 4

The U.S. Preventive Services Task Force gives this a B recommendation (moderate net benefit) based on evidence that treatment of screen-detected GDM significantly reduces preeclampsia, fetal macrosomia, and shoulder dystocia. 1

Two acceptable screening approaches:

1. Two-step approach (commonly used in US): 1, 3

   • 50g glucose challenge test (non-fasting) at 24-28 weeks
   • If ≥130-140 mg/dL at 1 hour → proceed to 100g OGTT
   • Diagnosis requires ≥2 abnormal values: fasting ≥95 mg/dL, 1-hr ≥180 mg/dL, 2-hr ≥155 mg/dL, 3-hr ≥140 mg/dL

2. One-step approach: 1, 3

   • 75g OGTT (fasting) at 24-28 weeks
   • Diagnosis requires only 1 abnormal value: fasting ≥92 mg/dL, 1-hr ≥180 mg/dL, or 2-hr ≥153 mg/dL

Evidence Against Early Screening in Average-Risk Women

The USPSTF explicitly states there is insufficient evidence to recommend screening before 24 weeks in average-risk women. 1, 3 Recent randomized controlled trial data suggests early screening in obese women does not necessarily improve perinatal outcomes compared to routine screening. 3

Iron Supplementation Recommendation: Routine Supplementation (Option B is Correct)

Routine iron supplementation during the second and third trimesters is recommended for all pregnant women to prevent anemia, as iron demand increases dramatically during pregnancy and most women cannot meet this demand through diet alone. 2

Important Caveat Regarding Iron Dosing

While routine iron supplementation is recommended, recent evidence suggests caution with high-dose iron (>30 mg/day for prolonged periods) in iron-replete women:

• Periconceptional iron supplementation >30 mg/day for >3 months was associated with 1.53-fold increased GDM risk (adjusted RR: 1.53,95% CI: 1.21-1.93). 5
• This association was even stronger (RR: 1.70) in primiparous, iron-replete women without family history of diabetes. 5
• A U-shaped relationship exists between serum iron concentration and GDM risk, with both very low and very high levels increasing risk. 6

Clinical implication: Iron supplementation should be given, but the dose and duration should be appropriate to the patient's iron status, avoiding excessive supplementation in iron-replete women. 5, 6

Common Pitfalls to Avoid

• Do not screen for GDM before 24 weeks in women without high-risk features, as this leads to unnecessary testing and potential overdiagnosis. 1, 3
• Do not skip screening at 24-28 weeks even in low-risk women, as universal screening is recommended and has proven benefit. 1, 3, 4
• Do not provide excessive iron supplementation (>30 mg/day long-term) without assessing iron status, particularly in iron-replete women. 5, 6