Molecular structure pattern

Gestational Diabetes Mellitus Initial Assessment

Clinical Presentation

Typically, gestational diabetes mellitus is asymptomatic early in pregnancy.

History

Obtain past medical history, obstetric outcomes, and family history of diabetes mellitus. Note for symptoms of polydipsia, polyuria, or polyphagia (suggesting a more severe hyperglycemia).

Physical Examination

Measure the patient’s weight and compute the body mass index (BMI).

Diagnosis or Diagnostic Criteria

The diagnostic criteria for overt diabetes mellitus (DM) and gestational diabetes mellitus at the first prenatal visit in women not known to have diabetes include:

  • Fasting plasma glucose (FPG) of ≥7 mmol/L (≥126 mg/dL) for overt DM
  • 5.1-6.9 mmol/L (92-125 mg/dL) for GDM


Other criteria for overt DM include:

  • A1c level of ≥6.5%
  • Random plasma glucose of ≥11.1 mmol/L (≥200 mg/dL)


Women who may be at risk of pre-pregnancy DM should be offered a 75-g oral glucose tolerance test (OGTT) at 24-28 weeks of gestation if the initial screening test is negative. 

Screening

Screening/Diagnosis of Gestational Diabetes Mellitus

Screening of gestational diabetes mellitus uses either the “one-step” or “two-step” approach. This is performed at 24-28 weeks of gestation in women without a previous diagnosis of overt diabetes. Consider offering the 75-g OGTT to women with clinical features of maternal hyperglycemia or those with risk factors but presented after 28 weeks of gestation.



Gestational Diabetes Mellitus_Initial AssesmentGestational Diabetes Mellitus_Initial Assesment




“One-step” Approach

The “one-step” approach diagnostic criterion is recommended by the World Health Organization (WHO) and derived from the International Association of Diabetes and Pregnancy Study Groups (IADPSG). A 2-hour 75-g oral glucose tolerance test (OGTT) is performed after an overnight fasting of at least 8 hours. Plasma glucose measurement at fasting and at 1 and 2 hours.

The diagnosis of gestational diabetes mellitus1 is made when any one of the following is present: 

  • FPG ≥5.1 mmol/L (≥92 mg/dL)
  • 1-hour plasma glucose ≥10 mmol/L (≥180 mg/dL)
  • 2-hour plasma glucose ≥8.5 mmol/L (≥153 mg/dL)

 

OGTT should be repeated 4-6 weeks later in patients with initial normal results. This may also be offered at 24-28 weeks in women with previous gestational diabetes mellitus.

The diagnostic criteria for overt DM using a 75-g 2-hour OGTT at 24-28 weeks of gestation are:

  • FPG of ≥7 mmol/L (126 mg/dL)
  • 2-hour plasma glucose of ≥11.1 mmol/L (200 mg/dL)

 

1The National Institute of Health and Care Excellence 2015 guideline (updated 2020) value for diagnosis of GDM with a 75-g 2-hour OGTT includes an FPG of ≥5.6 mmol/L or a 2-hour plasma glucose of ≥7.8 mmol/L.

“Two-step” Approach

The “two-step” approach diagnostic criterion is recommended by the American College of Obstetricians and Gynecologists (ACOG). A 50-g glucose 1-hour challenge test (non-fasting) followed by a 100-g 3-hour OGTT (fasting) for those with a positive screen is done. Perform a 100-g OGTT if the 1-hour plasma glucose level is ≥7.2, 7.5, or 7.8 mmol/L (≥130, 135, or 140 mg/dL).

The diagnosis of gestational diabetes mellitus is made when at least two of the following are present (ACOG notes that one elevated value can be used for diagnosis):

  • FPG ≥5.3 mmol/L (≥95 mg/dL)
  • 1-hour plasma glucose ≥10 mmol/L (≥180 mg/dL)
  • 2-hour plasma glucose ≥8.6 mmol/L (≥155 mg/dL)
  • 3-hour plasma glucose ≥7.8 mmol/L (≥140 mg/dL)