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Management> Pregnancy>
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Gestational Diabetes 

Wanda Nicholson, M.D.
02-04-2011

DEFINITION

  • Gestational diabetes mellitus (GDM) defined as glucose intolerance first identified during pregnancy, distinct from type 1 (T1DM) and type 2 diabetes mellitus (T2DM) which are initially diagnosed outside of pregnancy.

EPIDEMIOLOGY

  • GDM is the most common metabolic disease of pregnancy.
  • GDM affects an estimated 170,000 (1-14%) pregnancies each year in the United States, depending on the diagnostic criteria used and characteristics of the population (Jovanovic).
  • 30-50% of women with GDM will have recurrent GDM in a future pregnancy (Bellamy, Kim).
  • Of particular concern, 20-50% of women with GDM will develop T2DM in the 5-10 years after delivery (Jovanovic).
  • Recent meta-analysis reports that GDM corresponds to a 7.4 fold increased risk for developing T2DM (Bellamy).

DIAGNOSIS

  • At first prenatal visit, women at high risk of GDM (severe obesity, personal history of GDM or previous delivery of large-for-gestational age infant, glycosuria, PCOS or a strong family history of diabetes) should undergo standard diagnostic testing for diabetes. If abnormal, consider these individuals to have "overt" (not gestational) diabetes. If normal, retest between 24 - 28 weeks (ADA Standards of Medical Care 2010).
  • Low-risk women meeting all of the following criteria require no glucose testing: age <25 years, weight normal before pregnancy, member of an ethnic group with low prevalence of DM, no family history of diabetes, no personal history of abnormal glucose tolerance or adverse obstetric outcome.
  • Women of average risk should be tested at 24-28 weeks.
  • New ADA guidelines (2011): perform a 75-gram oral glucose tolerance test (OGTT), with plasma glucose measurement fasting and at 1 and 2 h at 24-28 weeks.
  • OGTT should be performed in the morning after an overnight fast of at least 8 hours.
  • The diagnosis of GDM is made when any of the following plasma glucose values are exceeded: fasting >92 mg/dl (5.1 mmol/l), 1 h >180 mg/dl (10.0 mmol/l) or 2 h >153 mg/dl (8.5 mmol/l).
  • Former criteria  for the diagnosis of GDM (i.e. Carpenter and Coustan) were based on three hour 100-gram OGTT.

Tables/Images

SIGNS AND SYMPTOMS

  • Classic signs and symptoms of hyperglycemia (such as polyuria, polydypsia, blurry vision, vaginal yeast infections) reflect blood glucose generally over 180 mg/dl. GDM, however, is frequently asymptomatic.

CLINICAL TREATMENT

Glucose control

  • Tight glycemic control is the primary goal, similar to targets in diabetic pregnancies in general.
  • Generally accepted goals for blood glucose levels during pregnancy are shown in Table 1.
Non-pharmacologic Management

  • The most important objective in managing GDM is to control maternal glycemia as close to normal as possible in order to reduce the chance of fetal loss, maternal and neonatal complications.
  • Obese women diagnosed with GDM should be started on a 30 kcal/kg/day American Diabetes Association (ADA) diet.
  • Carbohydrates should be restricted to 40-50% of diet.
  • Daily low-to-moderate intensity physical activity is recommended.
Pharmacologic Management

  • Should be initiated if dietary therapy alone fails. Insulin is considered the primary therapy.
  • Currently, the ADA and the American College of Obstetricians and Gynecologists do not endorse the use of oral anti-hyperglycemic agents during pregnancy and such therapy has not been approved by the Unites States Food and Drug Administration for treatment of GDM.
  • However, glyburide and metformin are still used for pharmacologic management in practice although insulin is preferred.
  • Metformin (Glucophage) primarily used up to 14 weeks in women with PCOS, shown to be safe throughout pregnancy in efficacy trial (Rowan).
  • No difference in maternal or neonatal outcomes with glyburide or metformin compared with insulin (Rowan, Nicholson, Langer, Moore).
  • See module on "Diabetic Pregnancy" for further information on insulin treatment.

FOLLOW UP

  • Can usually stop pharmacological therapy for GDM after delivery.
  • About 75% of women with GDM normalize glucose tolerance post-partum, but they have an increased risk of later T2DM.
  • ACOG and ADA recommends screening for diabetes at 6-12 wks post-partum.
  • If normal, assess glycemic status every 3 years.
  • Recent systematic review shows low sensitivity of fasting blood glucose as postpartum screening test for type 2 DM (Bennett).

EXPERT COMMENTS

  • Pregnancy always confers insulin resistance. Women with normal insulin secretion overcome this by increasing insulin output.
  • If a woman develops GDM, it signals subnormal insulin reserve.
  • Occasionally, T1DM presents during pregnancy, and the woman remains insulin-dependent post-partum, with unstable glycemia suggestive of T1DM.
  • New 2011 ADA criteria for diagnosis of GDM no longer suggest use of 50-gram screening OGTT, followed by 100-gram diagnostic OGTT; instead 75-gram OGTT alone is sufficient for both screening and diagnosis. These new criteria will significantly increase the prevalence of GDM, primarily because only one abnormal value, not two, is sufficient to make the diagnosis.

Basis for Recommendations

  • American Diabetes Association; Standards of medical care in diabetes--2011.; Diabetes Care; 2011; Vol. 34 Suppl 1; pp. S11-61;
    ISSN: 1935-5548;
    PUBMED: 21193625
    Rating: Basis for recommendation
    Comments:Describes American Diabetes Association guidelines on diagnosis and treatment of GDM.

REFERENCES

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