Gestational diabetes mellitus

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Contents

Introduction

Gestational diabetes mellitus (GDM, Gestational diabetes) is important as it increases risk of complications during pregnancy. It complicates about 5% of pregnancies.

Diagnosis

Diagnostic criteria can vary (internationally) causing some issues, not just in epidemiology:

  • Women with glucose levels in the upper ~5–10% of the population distribution.
    • Glucose concentrations that would be diagnostic of diabetes outside of pregnancy
    • Glucose concentrations associated with some increased risk of fetal morbidity.
      • Increasingly important following HAPO study which revealed strong, continuous association of maternal glucose levels from below those diagnostic of diabetes with increased birth weight and increased cord serum C-peptide levels[1]

Causes

Insulin resistance is believed to increase during pregnancy. This may be because of increased placental growth hormone and tumour necrosis factor alpha production as well as pre-existing mechanisms particularly associated with obesity such as increased phosphorylation of insulin receptor tyrosine or serine. It is believed that pregnancy-induced insulin resistance unmasks either:

  1. Autoimmune β-cell
    • Suspect in lean Caucasians and important as relatively rapid metabolic deterioration during or after pregnancy, so justify aggressive follow-up
  2. Genetic diabetes (essentially monogenetic diabetes mellitus leading to impaired insulin secretion
    • <5% of cases
  3. β-cell dysfunction associated with chronic insulin resistance
    • The majority

This is consistent with the observation that once pregnancy is over long term follow up shows a close to linear increase in the cumulative incidence of diabetes independent of ethnic group.

Complications

  • Excessive fetal growth
    • Birth trauma
    • Maternal morbidity from operative delivery (eg increased caesarean rate)
    • Suspected lifelong increased risks of glucose intolerance and obesity in offspring
  • Fetal mortality
  • Fetal morbidity with increased:

Intervention

After 24 weeks identification and intensive management of GDM is associated with a decrease in mortality and morbidity in infants[2] but the balance of benefits and harms of screening for GDM is still unclear[3]

  • Overtreatment of GDM with sustained levels of glucose below normal range may lead to small-for-gestational-age infants[4]
  • Serious neonatal morbidity is reduced[5] by treating those diagnosed on oral 75g oral GTT with:
    • Individualized medical nutrition therapy
    • Daily self-monitored blood glucose
    • Insulin if needed
  • Metformin appears to be an acceptable alternative to insulin[6]

External link

References

  1. Metzger BE, Lowe LP, Dyer AR, Trimble ER, Chaovarindr U, Coustan DR, Hadden DR, McCance DR, Hod M, McIntyre HD, Oats JJ, Persson B, Rogers MS, Sacks DA. Hyperglycemia and adverse pregnancy outcomes. The New England journal of medicine. 2008 May 8; 358(19):1991-2002.(Link to article – subscription may be required.)
  2. Hillier TA, Vesco KK, Pedula KL, Beil TL, Whitlock EP, Pettitt DJ. Screening for gestational diabetes mellitus: a systematic review for the U.S. Preventive Services Task Force. Annals of internal medicine. 2008 May 20; 148(10):766-75.
  3. Screening for gestational diabetes mellitus: U.S. Preventive Services Task Force recommendation statement. Annals of internal medicine. 2008 May 20; 148(10):759-65.
  4. Metzger BE, Buchanan TA, Coustan DR, de Leiva A, Dunger DB, Hadden DR, Hod M, Kitzmiller JL, Kjos SL, Oats JN, Pettitt DJ, Sacks DA, Zoupas C. Summary and recommendations of the Fifth International Workshop-Conference on Gestational Diabetes Mellitus. Diabetes care. 2007 Jul; 30 Suppl 2:S251-60.(Link to article – subscription may be required.)
  5. Metzger BE, Buchanan TA, Coustan DR, de Leiva A, Dunger DB, Hadden DR, Hod M, Kitzmiller JL, Kjos SL, Oats JN, Pettitt DJ, Sacks DA, Zoupas C. Summary and recommendations of the Fifth International Workshop-Conference on Gestational Diabetes Mellitus. Diabetes care. 2007 Jul; 30 Suppl 2:S251-60.(Link to article – subscription may be required.)
  6. Rowan JA, Hague WM, Gao W, Battin MR, Moore MP. Metformin versus insulin for the treatment of gestational diabetes. The New England journal of medicine. 2008 May 8; 358(19):2003-15.(Link to article – subscription may be required.)

This article is a work in progress. Please feel free to contribute to it.

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