Introduction Gestational diabetes mellitus (GDM) poses a significant health concern due to the numerous risks it presents to both the mother and fetus. While serum ferritin typically declines in cases of iron deficiency anemia, which is common during pregnancy, it may increase in the presence of inflammation. This study aims to evaluate the significance of serum ferritin in the context of GDM, considering its multifaceted role in these interconnected conditions. Methodology This cross-sectional study included pregnant women attending an obstetrics clinic for an oral glucose tolerance test at Hospital Canselor Tuanku Muhriz in Kuala Lumpur, Malaysia. With consent, demographic data, risk factors for GDM, and blood samples were collected. Blood samples were analyzed for serum ferritin, fasting blood glucose, two-hour post-glucose levels, and full blood count. The assessment of risk factors for GDM and the diagnosis of GDM adhered to Malaysian guidelines. The Mann-Whitney U test was employed to compare variables between the GDM and non-gestational diabetes mellitus (non-GDM) groups. Additionally, univariate and multivariate regression analyses were conducted to investigate the role of serum ferritin in GDM. All analyses were performed using IBM SPSS Statistics for Windows, Version 28.0 (Released 2021; IBM Corp., Armonk, NY, USA), with statistical significance set at p < 0.05. Results Among 172 pregnant women with an average gestational age of 23.6 weeks, the incidence of GDM was higher in those with risk factors (84.8%) compared to non-GDM participants (75.5%). Women with GDM had a slightly higher mean serum ferritin level (50.24 ± 29.00 ng/mL) than those without GDM (45.00 ± 58.69 ng/mL). However, ferritin levels did not significantly differ between the GDM and non-GDM groups (p = 0.669) or between those with and without risk factors (p = 0.374). While a higher BMI (OR: 0.832, p = 0.017) and ferritin (OR: 1.022, p = 0.031) levels independently predicted GDM, the predictive value of ferritin was borderline significant when combined with glucose tests (area under the curve = 0.689, p = 0.051). Conclusions Higher maternal serum ferritin levels in the mid-trimester are associated with increased BMI and GDM. However, maternal serum ferritin is most effective at predicting the incidence of GDM when used alongside standard glucose measurements, especially in women with elevated BMI.