["Innovative methods are warranted to optimize prenatal outcomes. This study's objective was to determine if a web-based behavioral intervention (BI) can prevent excessive gestational weight gain (GWG) by increasing physical activity (PA).", 'Participants were randomized to usual care (UC; n = 21) or BI (n = 24) between 10 to 14 weeks gestation. GWG, PA, and diet were assessed at baseline, mid-, and late pregnancy.', 'No differences in GWG or adherence to GWG recommendations presented between groups. Total UC MET-minutes significantly decreased from baseline to late-pregnancy (1,234 ± 372 MET-minutes, P = .013). Mid-pregnancy sustained PA was greater for BI than UC (20-minute PA bouts: 122 ± 106 vs. 46 ± 48 minutes/week, P = .005; 30-minute PA bouts: 74 ± 70 vs. 14 ± 24 minutes/week, P < .001), and greater for BI at mid-pregnancy compared with baseline (20-minute PA bouts: 61.3 ± 21.9; 30-minute PA bouts: 39.6 ± 14.8, both P < .05). BI energy intake at mid-pregnancy significantly increased from baseline (336 ± 127 kcals, P = .04) and was significantly greater than UC (2,503 ± 703 vs. 1,894 ± 594, P = .005).'] Does web-Based Behavioral Intervention Increases Maternal Exercise but Prevent Excessive Gestational Weight Gain in Previously Sedentary Women?