gestational%20diabetes%20mellitus
GESTATIONAL DIABETES MELLITUS
Gestational diabetes mellitus (GDM) is any degree of glucose intolerance with onset or first recognition during pregnancy.
Hyperglycemia in pregnancy may be suggested by the presence of glycosuria, a fetus that is large for date, or polyhydramnios.
Overt diabetes mellitus may be found in women presenting with risk factors for type 2 diabetes during the first prenatal visit (before 13 weeks of gestation).

Diagnosis

Overt Diabetes Mellitus (DM)

  • Diabetes diagnosed in the 1st trimester of pregnancy is classified as pre-existing pregestational diabetes 
  • Overt DM may be found in women presenting with risk factors for type 2 diabetes during the 1st prenatal visit (before 13 weeks of gestation) 
  • Risk factors for type 2 DM include:
    • Overweight
    • Physically inactive
    • History of gestational diabetes mellitus (GDM)
    • With hypertension, history of CVD, or polycystic ovary syndrome, acanthosis nigricans
    • HDL cholesterol level 0.90 mmol/L (<35 mg/dL) and/or triglyceride level 2.82 mmol/L (>250 mg/dL)
    • With previous test result that showed HbA1c ≥5.7%, impaired glucose tolerance or impaired fasting glucose
    • With DM in 1st-degree relative
    • Glycosuria at 1st prenatal visit
  • Diagnostic criteria for overt DM and GDM at the 1st prenatal visit in women not known to have diabetes include a fasting plasma glucose (FPG) of ≥7 mmol/L (≥126 mg/dL) for overt DM and 5.1-6.9 mmol/L (92-125 mg/dL)  for GDM  
    • Other criteria for overt DM include an HbA1c level of ≥6.5% and a 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 initial screening test is negative 

Screening/Diagnosis of Gestational Diabetes Mellitus (GDM)

  • Uses either the “one-step” or “two-step” approach 
  • Performed at 24-28 weeks of gestation in women without previous diagnosis of overt diabetes
    • Consider offering the 75-g OGTT to women with clinical features of maternal hyperglycemia or those with risk factor but presented after 28 weeks of gestation

“One-step” Approach

  • Diagnostic criterion recommended by WHO 
  • A 75-g oral glucose tolerance test (OGTT) is performed after an overnight fasting of 8-14 hours
  • Perform OGTT in the morning after an overnight fasting of at least 8 hours
  • Plasma glucose measurement at fasting and at 1 and 2 hours
  • Diagnosis of GDM1 is made when any 1 of the following is present:
    • FPG 5.1-6.9 mmol/L (92-125 mg/dL)
    • 1-hour plasma glucose ≥10 mmol/L (≥180 mg/dL)
    • 2-hour plasma glucose 8.5-11 mmol/L (153-199 mg/dL)
  • OGTT should be repeated 4-6 weeks later in patients with initial normal results
  • May also be offered at 24-28 weeks in women with previous GDM
  • Diagnostic criteria for overt DM using a 75-g 2-hour OGTT at 24-28 weeks of gestation are an FPG of ≥7 mmol/L (126 mg/dL) and a 2-hour plasma glucose of ≥11.1 mmol/L (200 mg/dL) 
  • 1National Institute of Health and Care Excellence 2015 guideline 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

  • Diagnostic criterion recommended by the American Congress 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 positive screen
    • Perform 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)  
  • Diagnosis of GDM is made when at least 2 of the following are present:
    • 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)

Postpartum Screening

  • All women who will be identified to have overt DM during pregnancy or have GDM should have postpartum glucose testing
    • Women with GDM should be screened for persistent DM 4-12 weeks postpartum as the risk of developing maternal type 2 diabetes is increased after pregnancy and also because GDM may be an undiagnosed pre-existing type 1 or 2 diabetes
      • Probability of progression to DM is high with the following postnatal test results: Impaired glucose tolerance with 75-g OGTT, HbA1c 5.7-6.4%, FPG 5.7-6.9 mmol/L 
    • Uses the fasting plasma glucose test and nonpregnancy diagnostic criteria
    • A 75-g 2-hour OGTT is not routinely offered in women with normal postpartum blood glucose levels
    • A1c is not advised for diagnosis of postpartum-persistent diabetes; may be offered at 1 year postpartum in women with GDM who have negative postnatal test for diabetes
    • Lifelong screening for development of DM or prediabetes at least every 3 years is recommended to all women with history of GDM with screening frequency depending on other risk factors

 

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