Pregnant women with mildly abnormal blood sugar levels at higher risk of developing type 2 diabetes

Gestational diabetes happens in more than three per cent of pregnancies in Ontario. Usually the condition resolves itself after delivery, but many studies have shown that these women are at a very high risk for developing "regular" type 2 diabetes later in life. New research out of the Institute for Clinical Evaluative Sciences (ICES) has found that even women with mild abnormalities in their blood sugar during pregnancy, previously thought not to have any clinical significance, are 2.5 times more likely to develop type 2 diabetes compared to those who had completely normal glucose testing.

* To test for gestational diabetes, women receive a glucose challenge test (GCT) in the late second trimester of pregnancy. If the result of this test is abnormal, they go on to have a diagnostic test, called the oral glucose tolerance test (OGTT). If this test does not show gestational diabetes, women are reassured their glucose levels are normal and that no further testing is needed.

* However, recent studies have suggested that women who have even mild abnormalities on either the GCT or the OGTT do actually have subtle differences in their metabolism after pregnancy.

* The study examined 15,000 pregnant women aged 20-49 in Ontario who had a mild abnormality on their GCT but did not ultimately get diagnosed with gestational diabetes. They were compared to about 60,000 pregnant women who did not have abnormalities on their GCT. The women were followed for 6.4 years after delivery, and those who had had an abnormal GCT were 2.5 times more likely to develop type 2 diabetes compared to those who had not had an abnormal GCT.

"These results show that even a mild abnormality in glucose testing during pregnancy is associated with an increased risk of diabetes later in life. Although we already know that women who've had gestational diabetes need to be monitored, the study suggests that even women with mild glucose abnormalities might benefit from diabetes prevention and detection strategies," says Baiju Shah, ICES researcher.

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Author affiliations: ICES (Shah), Mount Sinai Hospital (Retnakaran), Sunnybrook Health Sciences Centre (Shah); Ontario.

The study "Abnormal Screening Glucose Challenge Test in Pregnancy and Future Risk of Diabetes in Young Women" is in the May, 2009 issue of Diabetic Medicine.

More detailed study findings on the ICES website: www.ices.on.ca

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of health care issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting health care needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.