Excessive weight gain during pregnancy affects half of women with overweight or obesity, creating cascading health risks for both mother and child that extend well beyond delivery. This reality has driven urgent searches for scalable interventions that can reach women where they are, using technology they already carry. A comprehensive mobile health program combining smartphone apps, wireless monitoring devices, and adaptive coaching successfully reduced excessive gestational weight gain among 1,265 pregnant women with elevated BMI. The intervention used personalized automated feedback on weight and activity patterns, delivered through a smartphone application paired with wireless scales and fitness trackers. Women also received 13 weekly educational modules and step-wise support from lifestyle coaches when weight gain accelerated beyond healthy parameters. Clinicians received motivational interviewing training to enhance their discussions about appropriate weight gain targets. The digital approach represents a significant advance in prenatal care delivery, offering continuous support between clinical visits when most weight-related decisions occur. Current prenatal care typically provides only periodic weight checks without real-time feedback or behavioral guidance. This intervention's success suggests that combining passive monitoring with active coaching can meaningfully alter pregnancy outcomes. The scalability factor is particularly compelling given the widespread nature of excessive gestational weight gain. However, the study population was limited to women already engaged with an integrated health system, potentially excluding those at highest risk. The intervention's effectiveness in diverse healthcare settings and among women with limited technology access remains to be established.