Amy Aronovitz, M.D., and Boyd E. Metzger, M.D.
Northwestern University Feinberg School of Medicine

Definition/Key Clinical Features
Differential Diagnosis
Best Tests
Best Therapy
Best References

Definition/Key Clinical Features

• Glucose intolerance first identified during pregnancy
• Affects 5%–7% of pregnant women, and incidence is increasing
• Likely reverts to normal after delivery
• Associated with high risk of future glucose intolerance during pregnancy and diabetes outside of pregnancy (~ 50% within 5 yr)
• Risks to fetus include perinatal mortality, macrosomia, obesity, abnormal glucose metabolism, hypoglycemia, hypocalcemia, jaundice

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• Type 1 diabetes
• Type 2 diabetes

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Best Tests

• Assess patient's risk of gestational diabetes mellitus (GDM)
  • Low risk: blood glucose testing not routinely required
    • Patient exhibits all of the following characteristics:
      • Member of an ethnic group with low GDM prevalence
      • No known diabetes in first-degree relatives
      • Age < 25 yr
      • Normal weight before pregnancy
      • Normal weight at birth
      • No history of abnormal glucose metabolism
    • Fewer than 10% of women in the United States fit into this category
  • Average risk: test blood glucose at 24–28 wk gestation
    • All patients not classified as low or high risk are considered to be at average risk
  • High risk: test blood glucose as soon as possible and repeat at 24–28 weeks if initial tests negative
    • Patient has marked obesity; strong family history of type 2 diabetes mellitus; or history of GDM, impaired glucose metabolism, or glucosuria
• Two-step testing
  • Glucose challenge test (GCT): measure plasma glucose level 1 hr after ingestion of 50 g glucose
  • If plasma glucose > 140 mg/dl on GCT, perform 3-hr 100 g oral glucose tolerance test (OGTT); see criteria below
• One-step testing: OGTT only; diagnosis of GDM requires that plasma glucose levels meet two of the following criteria:
  • Fasting: > 95 mg/dl
  • 1 hr after 100 g oral glucose: ≥ 180 mg/dl
  • 2 hr after 100 g oral glucose: ≥ 155 mg/dl
  • 3 hr after 100 g oral glucose: ≥ 140 mg/dl
• Random plasma glucose level > 200 mg/dl and/or fasting plasma glucose >126 mg/dl, confirmed by second test, is also diagnostic

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• There are no randomized trials to identify blood glucose targets to prevent perinatal morbidity, but some evidence supports use of the following targets:
  • Fasting capillary blood glucose < 95 mg/dl, 1 hr postprandial < 140 mg/dl, 2 hr postprandial < 120 mg/dl
  • Focus efforts on women whose fetal abdominal circumference is ≥ 75th percentile

• Self-testing of capillary blood glucose

• Nutrition
  • Weight gain
    • Prepregnancy BMI ≥ 30 kg/m²: limit gain to 15 kg
    • Prepregnancy BMI < 18.5 kg/m²: gain of up to 18 kg
    • If desired weight gain achieved by the time of diagnosis, restrict intake to 25 kcal/kg
  • Restrict carbohydrates to 40%–45% of diet, but ≥ 180 g/day
  • Consume complex carbohydrates
  • Reduce or eliminate monosaccharides, sucrose, and other oligosaccharides from the diet
• Exercise
  • Assess baseline health and physical capacity
  • Three exercise sessions per wk, ≥ 15 min each
  • Improved blood glucose levels may not be seen until regimen has been maintained for 2–4 wk

• Begin if glycemic targets not maintained or if excessive fetal growth occurs
• NPH insulin: to control fasting hyperglycemia
  • 10–15 units at bedtime
  • Adjust dose to maintain fasting blood glucose of 60–90 mg/dl
  • Measure blood glucose between 2 A.M. and 4 A.M. to assess nocturnal hypoglycemia
• Regular or rapid-action insulin: to control postprandial hyperglycemia
  • Use when > 20%–25% of blood glucose tests register > 140 mg/dl at 1 hr after starting meal or > 120 mg/dl at 2 hr after meal
  • Inject 1 unit per 10 g anticipated carbohydrate intake
  • Regular insulin should be taken 40–60 min before meal; rapid-action insulin analogues should be taken 0–15 min before meal
  • Adjust dose according to postprandial blood glucose levels
• Goals for capillary whole blood glucose levels
  • Fasting: 60–90 mg/dl
  • Preprandial: 60–105 mg/dl
  • 1 hr after meal: < 140 mg/dl
  • 2 hr after meal: < 120 mg/dl
  • Goals difficult to achieve with current therapeutic tools

• Glyburide: effective alternative to insulin therapy
  • Dose: 2.5 mg q.d. initially; increase weekly in 5 mg increments to maximum of 20 mg q.d. in divided doses or until glycemic control attained
  • Monitor glucose levels closely to ensure adequate glycemic control
  • Cost/mo: $24
• Metformin: safety and efficacy during pregnancy not established

• Measure fasting and/or postprandial blood glucose shortly after delivery and perform an OGTT at 6 wk postpartum
• Assess annually for diabetes and metabolic syndrome
• Perform OGTT before subsequent pregnancies
• Use appropriate diabetes-prevention measures

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Best References

Metzger BE, et al: Diabetes Care 21(suppl 2):B161, 1998 [PMID 9704245]

Crowther CA, et al: N Engl J Med 352:2477, 2005 [PMID 15951574]

Langer O, et al: N Engl J Med 343:1134, 2000 [PMID 11036118]

National Diaetes Education Program

http://www.ndep.nih.gov/diabetes/pubs/NeverTooEarly_Tipsheet.pdf

Amy Aronovitz, M.D., has no commercial relationships with manufacturers of products or providers of services discussed in this module. Boyd E. Metzger, M.D., is a consultant to Sanofi Aventis.

January 2007