Objective: This study was based on a gestational diabetes mellitus (GDM) cohort in Shanghai to examine the association between physical exercise and plasma glucose control among GDM women with and determine what the effects of pre-pregnancy body mass index (BMI). 
Methods: In this study, GDM was diagnosed if the plasma glucose values at any of the following time points reached the diagnostic threshold: fasting blood glucose (5.1 mmol/L), 1-hour blood glucose (10.0 mmol/L), and 2-hour blood glucose (8.5 mmol/L) by 75 g oral glucose tolerance test (OGTT). Information on GDM women was extracted from the hospital’s health records and prenatal examination forms and was obtained through face-to-face interviews after delivery. A restricted cubic spline curve with four knots was used to flexibly model the relationship between the duration of moderate-intensity physical exercise and the percentage of abnormal plasma glucose among GDM patients with different BMI values. In this study, a P-value less than 0.05 (two-tailed) was considered as statistical significance. 
Results: Among 1139 GDM women with GDM, the median percentage of abnormal plasma glucose (PG) was 40.0% (interquartile range (IQR): 20.0– 66.7%), and the difference between overweight-obese group and underweight-normal group was statistically significant (50.0% vs 40.0%, P < 0.001). In this study, engaging in more physical exercise during pregnancy contributed to a higher prevalence of satisfactory glycemic control, and women with BMI < 25 kg/m² should engage in no less than 90 minutes of moderate-intensity physical activity per day to achieve satisfactory glycemic control (prevalence of abnormal PG < 35%). However, over 120 minutes of daily moderate-intensity physical activity is required for GDM women with a BMI ≥ 25 kg/m² to achieve satisfactory glycemic control. 
Conclusion: Overweight or obese women with GDM have a higher risk of poor glycemic control and require a longer duration of physical exercise to achieve the same level of blood glucose control.