Figure 1. Dose-Response Association of Moderate-to-Vigorous-Intensity Physical Activity (MVPA) With Preterm Birth.

A, Logistic regression was used to estimate the difference in odds ratios (ORs) of preterm birth between the physically active groups (MVPA ≥30 min/d) and inactive group (MVPA <30 min/d). The model was adjusted for physical activity energy expenditure, age, gestational week at baseline, prepregnancy body mass index, household income, educational level, smoking, alcohol drinking, and parity. B, Restricted cubic spline analysis was used to assess the shape of the association between MVPA and preterm delivery, adjusting for the same set of confounders as the aforementioned logistic regression. Here, MVPA equal to 30 minutes per day served as the reference. The y-axis represents the OR of preterm birth, with the shaded area indicating the corresponding 95% CIs.