British researchers report, that in women with gestational diabetes, a postnatal oral glucose tolerance test (OGTT) may only be necessary in women whose postnatal fasting plasma glucose is 6.0 mmol/L or more
This finding could spare the need for an OGTT in more than 90% of women with gestational diabetes, they add.
Women with gestational diabetes (GDM) are advised to undergo a postnatal OGTT 6 weeks after delivery. But compared to the fasting plasma glucose test, the OGTT is time-consuming, unpleasant, and relatively expensive.
"Furthermore, as the prevalence of postnatal diabetes is low in our population (2.4%), we questioned the value of performing postnatal OGTTs on all women with a history of GDM," note Richard I. G. Holt, MD, with the Foetal Origins of Adult Disease Division and Health Care Research Unit, University of Southampton, in Southampton, United Kingdom, and colleagues.
Dr. Holt and colleagues attempted to identify whether fasting plasma glucose 6 weeks after delivery could identify which women should also undergo a postnatal OGTT.
They evaluated 152 women who were diagnosed with GDM according to World Health Organization criteria and were advised to have an OGTT 6 weeks postpartum. They then assessed the results of the fasting plasma glucose concentration in relation to the 2-hour glucose value from the OGTT.
Of the participants, 19.7% chose not to undergo an OGTT. Among the remainder, three women had diabetes, three had impaired glucose tolerance, and four had impaired fasting glycaemia.
None of the women with a normal OGTT level had fasting glucose of 6.0 mmol/L or more, and the two tests were well correlated (r=0.62, P<0.0001). According to the researchers, only 8.1% of the OGTTs would have been performed if only women with fasting glucose of 6.0 mmol/L or greater underwent the test.
"The sensitivity and specificity of this approach for the diagnosis of postnatal diabetes is 100% and 94%, respectively," they report, and they estimate that selecting women in this way would miss fewer than three in 10,000 cases.
Dr. Holt and colleagues point out that while the two tests are well correlated, some groups of individuals are more likely to be identified by plasma fasting glucose levels than others.
"Those who are more likely to be identified by the (OGTT) include the elderly and certain non-Caucasian ethnic groups. On the other hand, middle-aged more obese patients are more likely to have diagnostic fasting values," they note. Diabet Med 2003;20:7:594-598.
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