Objective:To study the determinants of Gestational Diabetes Mellitus (GDM).Design:Case-control study. Setting: Sri Avittom Thirunal Hospital, Thiruvananthapuram district, Kerala, South India.Participants:300 GDM women as cases and 300 age-matched controls.Study variables:Sociodemographic characteristics, pre-pregnancy Body Mass Index (BMI), menstrual history, obstetric history, infertility history, family history of diabetes in first degree relatives, recurrent urinary tract infection (UTI), and moniliasis.Statistical analysis:T-test, Fishers Exact Test, Chi square test, Adjusted Odds Ratio with 95% CI. Results: Pre-pregnancy BMI ≥ 25 (P < 0.001, OR = 2.7), irregular menstrual cycle (P = 0.006), treatment for infertility (P = 0.001, OR = 3.3), family history of diabetes (P = 0.001, OR = 4.5), history of diabetes in mother (P = 0.003), previous pregnancy losses (P = 0.04), past GDM (P = 0.035), prematurity (P = 0.01), pre-eclampsia (P = 0.04), polyhydramnios (P < 0.001, OR = 6.0), UTI (P < 0.001, OR = 3.2), and moniliasis (P < 0.001, OR = 7.6) were significantly associated with present GDM.Conclusion:Early identification of women at risk of GDM and prompt treatment is recommended to prevent complications.

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