Introduction: Normal pregnancy is a diabetogenic state since during pregnancy there is an increase in insulin resistance. Gestational diabetes mellitus (GDM) is now emerging as the most common medical complication during pregnancy which leads to serious consequences. It is observed that women with GDM had a 7 times higher chance of manifestation of developing impaired glucose tolerance (IGT) or type 2 diabetes mellitus (T2DM) during the later part of life. The present study was planned to find out the association between HbA1c level before 14 weeks of gestation and cut-off values for better pregnancy outcomes. Materials and methods: This hospital-based prospective observational study was conducted with 112 patients at the Department of Obstetrics and Gynaecology, Aarupadai Veedu Medical College & Hospital, Vinayaka Mission's Research Foundation (Deemed to be University), Puducherry, India, during the period of January 2021 to June 2022. Healthy 112 patients fulfilling the inclusion criteria were included in this study. The patient was asked to undergo screening for GDM at 24–26 weeks of gestation [International Association of Diabetes and Pregnancy Study Groups (IADPSG)]. Patients were followed up closely throughout pregnancy till delivery and 5 days postnatal period. Chi-square test and multivariate analysis were adapted to analyze the data by using the statistical package for the social sciences (SPSS), version 25.0, software. Results: A total of 112 participants fulfilling the criteria for inclusion were evaluated for HbA1c levels during pregnancy. The oral glucose tolerance test (OGTT) was used for the detection of gestational diabetes between 24 and 28 weeks. The occurrence of GDM in the study population is 23.5%. The participants who had HbA1c ≥ 5.7% developed maternal, fetal, and neonatal complications. In the present study, it was observed that HbA1c ≥ 5.7% has a sensitivity of 89% and specificity of 80%. Conclusion: The HbA1c value estimated during early pregnancy (<14 weeks) is useful in the prediction of GDM and it correlates well with adverse pregnancy outcomes. The cut-off value of 5.7% can be used for the prediction of GDM with good sensitivity and specificity. It can be an additional screening tool for GDM in addition to OGTT.