Received on July 22, 2005
Accepted on June 30, 2006

Evidence-Based Laboratory Medicine and Test Utilization

Lack of Concordance between the 75-g and 100-g Glucose Load Tests for the Diagnosis of Gestational Diabetes Mellitus

¹ Department of Gynecology, Perinatology and Human Reproduction, University of Florence, Firenze, Italy
² Department of Laboratory, Clinical Chemistry Laboratory, Azienda Ospedaliera-Universitaria Careggi, Firenze, Italy
³ Department of Statistics and Mathematics Applied to Economics, University of Pisa, Pisa, Italy

^* To whom correspondence should be addressed. E-mail: a.ognibene{at}tin.it.

Background: Gestational diabetes mellitus (GDM) is common and can have a substantial impact on fetal growth, birth weight, and morbidity. The American Diabetes Association recommends GDM testing with either a 3-h, 100-g glucose load (100g) (criteria according to Am J Obstet Gynecol 1982;144:768-73) or a 2-h, 75-g glucose load (75g). We investigated the comparability of the 75g and the 100g tests in the diagnosis of GDM.

Methods: From January 1997 to December 1999, in 1061 consecutive Caucasian nonobese and nondiabetic pregnant women who attended the Maternal-Fetal Medicine Unit, we performed GDM testing with a 75-g load during 2 periods of pregnancy: early (16-20 weeks) and late (26-30 weeks). Because we assumed there would be few GBM cases in women with a 1-h plasma glucose <1300 mg/L in the 75g test, we did not retest these women. We retested the remaining women with possible or diagnosed GDM with a 100-g load within a week.

Results: GDM was diagnosed in 41 of 227 women with the 100-g load and 15 of 227 with the 75-g load (11 concordant); the index was 0.21. At 26-31 weeks of pregnancy, 484 of 976 women (49.9%) underwent both tests. GDM was diagnosed in 60 of 484 woman with the 100-g load and in 26 of 484 with the 75-g load (13 concordant); the index was 0.18.

Conclusions: Among women with possible GDM in both early and late periods of pregnancy, there was only weak diagnostic agreement between results determined with 75-g and 100-g glucose loads.