Objective: To evaluate data from a five-year period (2014-2018) regarding the presence of thyroid dysfunction and thyroid antibodies among subjects with gestational diabetes mellitus (GDM) and pre-gestational diabetes mellitus (pre-GDM) at King Abdulaziz University Hospital (KAUH), Jeddah, Saudi Arabia (SA). Subjects and Methods: The present retrospective analysis was conducted from January to June 2019; it evaluated five years’ (2014-2018) data of patients with GDM and pre-GDM from the patients’ electronic record. Results: Of the 485 subjects, 348 (71.8%) were Saudi nationals; whereas, 137 (28.2%) were non-Saudis, and 318 (65.6%) had GDM and 167 (34.4%) had pre-GDM. Five (3.2%) hyperthyroid subjects were in the GDM group as compared to 6 (4.7%) in the pre-GDM group; whereas, 21 (13.3%) hypothyroid subjects were found in the GDM group as compared to 26 (20.3%) in the pre-GDM group. Thyroglobulin antibody (TgAb) was positive among 6 (4.7%) pre-GDM subjects as compared to 2 (1.3%) among GDM subjects (p=0.03). In the GDM group, 5 (3.2%) subjects had positive thyroid peroxidase antibody (TPOAb); whereas, in the pre-GDM group, 7 (5.5%) were TPOAb-positive (p=0.54). TgAb was positive among 1 (0.44%), 3 (27.27%), and 4 (8.51%) euthyroid, hyperthyroid, and hypothyroid subjects, respectively. TPOAb was positive among 4 (1.76%), 4 (36.36%), and 4 (8.51%) euthyroid, hyperthyroid, and hypothyroid subjects, respectively. Thyroid dysfunction was more common in pregnant females of age range 35-44.9 years. Conclusions: Hypo- and hyperthyroid cases were present in both GDM and pre-GDM groups. Thyroid antibodies were found more frequently in the pre-GDM group, and thyroid dysfunction was more common in the older age group.