Glucose Tolerance: Gestational Diabetes Mellitus

American Diabetes Association (ADA) Recommendations

Note: The American College of Obstetricians and Gynecologists maintains a different set of recommendations for the screen and diagnosis of gestational diabetes mellitus. The ACOG recommendations follow below.

Rationale: The American Diabetes Association (ADA) 2015 Standards of Medical Care provide the following recommendations regarding the diagnosis of gestational diabetes mellitus.^1,2

Screen for undiagnosed type 2 diabetes at the first prenatal visit in those with risk factors, using criteria described for diabetes mellitus.

In pregnant women not known to have diabetes, screen for gestational diabetes mellitus (GDM) at 24 to 28 weeks of gestation, using the Gestational Glucose Tolerance Screening and Diagnostics Test (Two-hour, ADA Recommendations) (101000). The diagnosis is made when any of the following plasma glucose values are exceeded:

• Fasting glucose ≥92 mg/dL
• One-hour glucose ≥180 mg/dL
• Two-hour glucose ≥153 mg/dL

Screen women with GDM for persistent diabetes 6 to 12 weeks postpartum using the criteria described under nongestational diabetes mellitus.

Women with a history of GDM should have lifelong screening for the development of diabetes or prediabetes at least every three years using the criteria described for nongestational diabetes mellitus.

American College of Obstetricians and Gynecologists (ACOG) Recommendations

Rationale: The American College of Obstetricians and Gynecologists provides the following recommendations regarding the diagnosis of gestational diabetes mellitus.³

All pregnant women should be screened for gestational diabetes mellitus—whether by patient history, clinical risk factors, or with a 50-gram, one-hour loading test at 24 to 28 weeks of gestation to determine blood glucose levels (102277).

The diagnosis of GDM can be made based on the result of the 100-g, three-hour oral glucose tolerance test (102004). Either the plasma or serum glucose levels established by Carpenter and Coustan or the plasma levels designated by the National Diabetes Data Group are appropriate to use (see table). A positive diagnosis requires that two or more upper thresholds be met or exceeded. LabCorp reference values for 102004 are those of the Carpenter and Coustan conversion.

 

Specimen*	Plasma or Serum Glucose Level (Carpenter and Coustan Conversion)	Plasma Glucose Level (National Diabetes Data Group Conversion)
*The diagnosis of GDM can be made based on the result of the 100-gram, three-hour oral glucose tolerance test, for which there is evidence that treatment improves outcome. Either the plasma or serum glucose level established by Carpenter and Coustan or the plasma level designated by the National Diabetes Data Group is appropriate to use. A positive diagnosis requires that two or more high thresholds be exceeded. The Carpenter and Coustan conversion is used to establish LabCorp reference intervals.
Fasting	65−94 mg/dL	65−105 mg/dL
One-hour	65−179 mg/dL	65−190 mg/dL
Two-hour	65−154 mg/dL	65−165 mg/dL
Three-hour	65−139 mg/dL	65−145 mg/dL

References

1. American Diabetes Association. Standards of Medical Care in Diabetes—2015: Summary of revisions. Diabetes Care. 2015 Jan; 38(Suppl 1):S1-S93. PubMed 25537706

2. World Health Organization. Definition, Diagnosis and Classification of Diabetes Mellitus and its Complications. Part 1: Diagnosis and a WHO Consultation. Geneva, Switzerland: WHO;1999. WHO/NCD/NCS/99.2.

3. The American College of Obstetricians and Gynecologists. Committee on Practice Bulletins—Obstetrics. Practice Bulletin N° 137: Gestational diabetes mellitus. Obstet Gynecol. 2013 Aug; 122(2 Pt 1):406-416751-753. PubMed 23969827