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Phaik Ling Quah,1 Lay Kok Tan,2 Ngee Lek,3,4 Serene Thain,2 Kok Hian Tan1,4 1Deparment of Obstetrics and Gynaecology, KK Women’s and Children’s Hospital, Singapore; 2Department of Maternal Fetal Medicine, KK Women’s and Children’s Hospital, Singapore; 3Department of Pediatrics, KK Women’s and Children’s Hospital, Singapore; 4OBGYN ACP, Duke-NUS Medical School, SingaporeCorrespondence: Phaik Ling Quah, Division of Obstetrics and Gynaecology, KK Women’s and Children’s Hospital (KKH), 100 Bukit Timah Road, 229899, Singapore, Tel +65 9773-2543, Email quah.phaik.ling@kkh.com.sgPurpose: This study examined the prospective association between CGM-derived glycemic variability (GV) and glycemic control (GC) parameters in the first and second trimester, with subsequent diagnosis of GDM in the early third trimester.Methods: In a longitudinal observational study, 60 study participants in the first trimester (9– 13 weeks’ gestation), and 53 participants (18– 23 weeks’ gestation) in the second trimester of pregnancy had CGM data extracted after a minimum of 8 days’ wear time (up to 14 days). At 24– 31 weeks’ gestation, participants underwent a 75 g, 2-hour oral glucose-tolerance test as per IADPSG criteria to diagnose GDM. GV parameters examined in both first and second trimesters were mean amplitude of glycemic excursion (MAGE), standard deviation (SD), mean glucose, and coefficient of variation (CV). GC parameters measured were J-Index and percentage of time spent in glucose target ranges.Results: The first trimester SD and MAGE were significantly higher in participants subsequently diagnosed with GDM (SD adjusted median 1.31 [interquartile range 1.2– 1.3] mmol/L; MAGE 3.26 [3.2– 3.3] mmol/L) than those who were not (SD 1.01 [0.9– 1.0] mmol/L, MAGE 2.59 [2.4– 2.6] mmol/L; p< 0.05). Similarly, second trimester SD and MAGE were also significantly higher in participants subsequently diagnosed with GDM (SD 1.35 [1.3– 1.4] mmol/L; MAGE 3.32 (3.31– 3.41) mmol/L) than those who were not (SD 0.99 [0.98– 1.01] mmol/L, MAGE 2.42 [2.42– 2.55] mmol/L; p< 0.05). Associations between SD and MAGE with GDM outcomes were adjusted for prepregnancy BMI and ethnicity. There were nonsignificant trends of higher J-Index scores in the first and second trimester, higher CV in the first trimester only, and higher mean in the second trimester only in participants diagnosed with GDM. Other study parameters measured were not significantly different between groups (p> 0.003).Conclusion: Our study suggests the potential value of CGM-derived SD and MAGE in early pregnancy as potential predictors of subsequent GDM diagnosis.Keywords: continuous glucose monitoring, glycemic parameters, glycemic control, diabetes in pregnancy