Background and Objectives: Overactive bladder (OAB) is a serious urination-related symptom of unknown pathogenesis that affects one’s everyday activities. The objective of this study was to examine how OAB prevalence, symptom severity, and degree of distress caused by OAB symptoms evolved throughout the course of pregnancy. Materials and Methods: A total of 659 pregnant women were recruited from 2015 to 2020, and were evaluated through the International Consultation on Incontinence Questionnaire-Overactive Bladder (ICIQ-OAB) on OAB symptoms, administered in the early, middle, and late stages of pregnancy. Results: Generalized estimating equation analysis revealed that the odds of OAB occurring in the middle and late stages of pregnancy were 1.90 and 2.33 times higher, respectively, than in early pregnancy. The corresponding odds for OAB-wet were 1.63 and 2.07 higher, respectively, and the odds of OAB-dry occurring during late pregnancy were 0.80 higher than during early pregnancy. Symptoms were more severe by 0.07 and 0.21 points (on a 4-point scale) in the middle and late stages of pregnancy, respectively, than in early pregnancy; distress was greater by 0.13 and 0.27 points (on a 10-point scale) in the middle and late stages of pregnancy, respectively, than in early pregnancy. The prevalence of OAB, OAB-dry, and OAB-wet was significantly higher in early pregnancy than pre-pregnancy. Conclusions: The prevalence of OAB and OAB-wet increased over the course of pregnancy, but the prevalence of OAB-dry decreased. Furthermore, symptom severity and degree of distress increased over time.