CLINICAL ACTIONS:

Professional organizations agree that all pregnant women should be screening for Gestational Diabetes Mellitus (GDM).  While there are varying approaches, ACOG and a consensus panel convened by the NIH have endorsed the following ‘2 step’ approach to screening for GDM:

STEP 1: All women should be screened for GDM between 24 and 28 weeks gestation with a 50g oral glucose solution followed by a 1 hour venous glucose measurement. Healthcare providers have the option of using the following values:

• 130 or 135 mg/dL – lower cut-off threshold – which may identify women who may have GDM but also increase false positive rates
• 140 mg/dL – higher cut-off threshold – which may limit the number of screen positive women, but may miss those with GDM

Screen earlier in pregnancy if high risk factors for GDM are identified:

Patient is overweight with BMI of 25 (23 in Asian Americans) and one of the following:

• Physical inactivity
• Known impaired glucose metabolism
• Previous pregnancy history of:
  • GDM
  • Macrosomia (≥ 4000 g)
  • Stillbirth
• Hypertension (140/90 mm Hg or being treated for hypertension)
• HDL cholesterol < 35 mg/dl (0.90 mmol/L)
• Triglyceride > 250 mg/dL (2.82 mmol/L)
• PCOS
• Hgb A_1C ≥ 5.7%, impaired glucose tolerance or impaired fasting glucose
• Cardiovascular disease
• Signs/symptoms suggesting increased risk for diabetes such as acanthosis nigricans or morbid obesity)
• Family history of diabetes – 1st degree relative
• Ethnicity of African American, American Indian, Asian American, Hispanic, Latina, or Pacific Islander

If a patient with risk factors is tested earlier and is screen negative, the patient should still be screened again between 24-28 weeks using the 50g oral glucose load.

STEP 2: If screen positive following STEP 1,  a diagnostic test, the 100g 3 hour oral glucose tolerance test (OGTT), is recommended. A diagnosis is made if at least two values are exceeded using one of two methods:

Note: ACOG recommends that currently there is insufficient evidence to diagnose GDM based on only one abnormal value | Patients with only one elevated value may require additional surveillance

National Diabetes Data Group

• Fasting ≥ 105 mg/dL  (5.8 mmol/l)
• 1-hour ≥ 190 mg/dL   (10.6 mmol/l)
• 2-hour ≥ 165 mg/dL   (9.2 mmol/l)
• 3-hour ≥ 145 mg/dL   (8.0 mmol/l)

Carpenter and Coustan

• Fasting ≥ 95 mg/dL (5.3 mmol/l)
• 1-hour ≥ 180 mg/dL (10.0 mmol/l)
• 2-hour ≥ 155 mg/dL (8.6 mmol/l)
• 3-hour ≥ 140 mg/dL (7.8 mmol/l)

SYNOPSIS:

GDM is a common complication of pregnancy. Aside from well-known complications associated with birth trauma and increased risk of operative delivery and preeclampsia, there may be long term complications including increased risk of obesity and diabetes later in life, although maternal obesity and excessive weight gain may be independent risk factors for macrosomia and childhood obesity. Treatment for GDM does appear to improve outcomes.  Screening all women is necessary as traditional risk factors may only detect 50% of GDM.

KEY POINTS:

• ACOG and consensus panel convened by the NIH do not recommend the ‘one step’ approach, but rather the ‘two step’ approach
• The ‘one-step’ screening approach will result is increased diagnosis of GDM
• Targeting obesity and improved nutrition can also address macrosomia risks

Learn More – Primary Sources:

ACOG Practice Bulletin No. 190: Gestational Diabetes Mellitus

Related ObG Topics:

GDM and Postpartum Followup – The ‘When and How’ of Screening

Addition of glyburide in mild GDM-is there benefit?

What Is The ‘One-Step’ GDM Screening Approach?

Gestational Diabetes Mellitus – Definitions, Risk Factors and Complications