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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Diabetes In Pregnancy Series
Sponsored by The Indian Health Service Clinical Support Center
PART 1: Screening and Diagnosis
5 Diagnosis
In the 2-step method, if a patient has a positive screen, the next step is to order the diagnostic test, which is the 100-g 3-hour OGTT. This must be administered in the fasting state and venous blood should be used.
Patients should eat their regular diet for several days prior to testing, as trying to restrict carbohydrates may result in a false positive test due to insulin down-regulation.
The National Diabetes Data Group (NDDG) have the largest data to recommend their use.
Fasting |
< 105 Plasma glucose level (mg/dL) |
1-hour |
< 190 Plasma glucose level (mg/dL) |
2-hour |
< 165 Plasma glucose level (mg/dL) |
3-hour |
< 145 Plasma glucose level (mg/dL) |
The diagnosis of GDM is made if the patient has met
or exceeded two values.
Patients with only one abnormal value, especially the two-hour plasma glucose
level, have also been shown to have an excess of perinatal morbidity, especially
macrosomia, and these patients have been designated as having "carbohydrate intolerance
of pregnancy", and may benefit from intervention, e.g., medical nutrition therapy
(Tallarigo
et al).
Screening may be repeated at 32 weeks, especially if there was one abnormal value on OGTT. (Neiger et al)
Multiple sets of diagnostic criteria exist. See Other diagnostic criteria. The newer, lower, criteria of Carpenter and Coustan have been suggested by the ADA, but no data from clinical trials has determined which is superior, and cost-effectiveness studies favor the NDDG criteria.
If all this seems cumbersome to you, you're not alone.
The World Health Organization (WHO) tried to unite criteria both in pregnancy and outside of pregnancy.
WHO uses a 2-hour OGTT with a 75-g glucose load followed by a fasting and 2-hour glucose. A 2-hour glucose > 140 mg/dL meets the criteria for Impaired Glucose Tolerance, but it is treated the same as GDM. The one step test would seem to simplify things considerably, but has not yet been adopted widely in the US yet (Pettitt et al 1994). See Other diagnostic criteria.
