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| |  Glucose Challenge During Pregnancy May Be Falsely Negative in Women With Family History of Diabetes: Presented at IDF By Brian Hoyle MONTREAL -- October 21, 2009 -- The glucose challenge test (GCT) -- a common screening performed at 24 to 26 weeks of pregnancy for gestational diabetes mellitus (GDM) -- may be falsely negative in pregnant women with a family history of diabetes, who may go on to develop GDM or gestational impaired glucose tolerance (GIGT), according to researchers at the 20th World Diabetes Congress of the International Diabetes Federation (IDF). These conclusions were part of a presentation here on October 19 led by Natalia Yakubovich MD, MSc, Mt. Sinai Hospital, Toronto, Ontario, and researchers from Mt. Sinai and St. Michael’s Hospital, Toronto, Ontario. In the GCT, a plasma glucose level of at least 7.8 mmol/L at 1 hour after an oral, 50-g dose of glucose prompts a definitive oral glucose tolerance test (OGTT). The test is often, but not always, reliable. Some pregnant women who present a negative GCT later develop GDM or GIGT. The consequences can include heightened risk for fetal macrosoma, adverse maternal-fetal outcome, and metabolic perturbations in mother and child. To clarify the underlying clinical characteristics of women with a false-negative GCT, a prospective longitudinal cohort study was performed involving 124 women who tested normally in the GCT. The subjects subsequently underwent two 3-hour OGTTs: one during pregnancy using 100 g of glucose, and the other 3 months after birth using 75 g of glucose. Ninety-three women maintained normal glucose tolerance throughout pregnancy and early post partum. Thirty-one women were diagnosed with GDM or GIGT (ie, the GCT result represented a false-negative). Age, ethnicity, body mass index prior to pregnancy, and GCT results were not significantly different between participants. But, of the 31 women who displayed a false-negative GCT, 64.5% had a family history of diabetes. Of the women whose glucose tolerance remained normal during pregnancy, significantly fewer (41.9%, P = .03) had a family history of diabetes. OGTT results 3 months after birth revealed significant changes in the false-negative GCT group: · Elevated fasting glucose (normal: 4.4, range 4.1-4.6; GDM/GIGT: 4.6, range 4.2-4.7; P = .04) At 3 months post partum, 12.9% of the false-negative group proved to be prediabetic -- a significantly higher number than the 3.2% of women whose glucose tolerance remained normal (P = .06). A comparison of clinical characteristics at the time of GCT demonstrated that the GCT result was not significant to the subsequent development of GDM or GIGT (odds ratio [OR] 1.45; 95% confidence interval [CI], 0.95-2.22; P = .08), but family history of diabetes was significant (OR 2.37; 95% CI, 1.01-5.57; P = .048). A normal GCT screening test may be falsely negative in women with a family history of diabetes, the researchers concluded, and the standard 1-hour GCT value “is a significant predictor of development of GDM or GIGT.” Further metabolic testing in pregnancy should be considered in these women, they noted. The “why” of a false-negative result, however, is still a mystery. “The issue now is to identify these particulars,” stated Dr. Yakubovich. In addition, fine-tuning the GCT is needed in terms of the optimal cutoff point to define a positive test that ultimately will more realistically account for false negative results. Funding for this study was provided by the Canadian Institutes for Health Research. [Presentation title: Screening Glucose Challenge Test in Pregnancy: Impact of Family History of Diabetes on the Likelihood of a False-Negative Result. Abstract D-0660]
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