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Background: diagnostic criteria for gestational diabetes mellitus (GDM) have been controversial. Although Oral Glucose Tolerant Test (OGTT) is generally proposed, it requires an extensive preparation, is uncomfortable and lacks reproducibility. In contrast, Glycated Hemoglobin test (A1C) is more convenient and accurate, however, its use for GDM diagnosis has not been recommended yet. The aim of this study was to evaluate whether a first trimester A1C predicts an abnormal second trimester OGTT. Methods: This was an observational retrospective study that included Brazilian women screened with A1C until 14 weeks of gestation between January 2009 and March 2019. Data were collected from a laboratory center. A1C was measured by high-performance liquid chromatography. Exclusion criteria were first trimester glycemia ≥ 92 mg/dL or A1C ≥ 6.5% and use of antidiabetic drugs or insulin. Primary outcome was association between A1C value and diagnosis of GDM, according to 75g or 100g OGTT, as defined by American Diabetes Association (ADA). Results: a total of 373 women were included, 106 were diagnosed with GDM by OGTT. General characteristics of the groups with and without GDM were, respectively: mean age 35.1 ±3.5 and 34.1 ± 3.5 years, mean Body Mass Index (BMI) 24.2 ± 4.8 and 25.4 ± 3.7 Kg/m², mean first trimester glycemia 81.8 ± 5.1 and 81.2 ± 5.2 mg/dL and mean A1C 5.1 ± 0.3 and 5.0 ± 0.3%. OGTT values in the GDM group were: fasting 80.1 ± 6.6, 1st hour 171.6 ± 25.7 and 2nd hour 152 ± 27.1. For women without GDM, the results were: fasting 78.1 ± 5.7, 1st h 143.4 ± 29.5 and 2nd h 123.1 ± 28.3. There was no significant statistical difference of A1C values between groups with or without GDM (P=0.26, Wilcoxon test). Conclusion: A1C could not predict women who would develop GDM in this population. Ethnicity and different criteria for OGTT interpretation may have contributed for these findings. The limitations of this study were lack of data about previous history of GDM, family history of diabetes and weight gain during pregnancy. Disclosure F. Faro: None. R.F. Ramalho: None. W.H. Prieto: None. M. Pereira: None. J.E. Salles: Board Member; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Lilly Diabetes, Novo Nordisk Inc. P.S. Rosa: None. M.G. Teles: None. P. de Sá Tavares Russo: None.

Background: first trimester glycemia ≥ 92 mg/dL is a valid criterion for diagnosis of gestational diabetes mellitus (GDM), excluding the requirement of Oral Glucose Tolerant Test (OGTT) later in pregnancy. Glycated Hemoglobin (A1C), is well stablished for diagnosis of diabetes mellitus, however its utility in the screening of GDM is not certain. The aim of this study was to associate A1C and glycemia values in the first trimester of pregnancy. Methods: this was an observational retrospective study that included Brazilian women screened with A1C until 20 weeks of gestation between January 2009 and March 2019. Data were collected from a laboratory center. A1C was estimated by high-performance liquid chromatography. Exclusion criteria were hemoglobin < 11.0 and use of antidiabetic drugs or insulin. Women were divided into groups according to first trimester glycemia: Results: a total of 17.764 women were included. The majority was in the 70-85 mg/dL group (9.689), followed by 85-92 mg/dL (5.420), 92-126 mg/dL (2.178), < 70 mg/dL (436) and ≥ 126 mg/dL (41). Means’ age were: 32.5 ± 4.79 ( Conclusion: in this study, A1C values were not accurate to the screening of GDM in the first trimester of pregnancy. The main difference was in the group with glycemia ≥ 126 mg/dL, already defined as overt diabetes. Disclosure F. Faro: None. R.F. Ramalho: None. M. Pereira: None. J.E. Salles: Board Member; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Lilly Diabetes, Novo Nordisk Inc. P.S. Rosa: None. M.G. Teles: None. P. de Sá Tavares Russo: None.