Objective <p>To systematically evaluate the effectiveness of mobile health (mHealth) interventions on physical activity in pregnant women and to explore key factors influencing the intervention outcomes.</p> Methods <p>A systematic search was conducted across databases including PubMed, Web of Science, MEDLINE, Embase, Cochrane Library, CINAHL, Scopus, CNKI, WanFang, and VIP to identify randomized controlled trials (RCTs) assessing the impact of mHealth interventions on physical activity during pregnancy. Study quality was assessed using the Cochrane Risk of Bias tool 2.0 (RoB 2.0). Meta-analysis, including the pooling of effect sizes (using Standardized Mean Difference, SMD) and prespecified subgroup analyses, was performed using RevMan 5.4 software. Due to the limited number of included studies, exploratory meta-regression was conducted as a supplementary analysis and its results were interpreted with caution. No formal statistical tests for publication bias were performed.</p> Results <p>Sixteen studies were included in the qualitative synthesis, of which ten studies (1,615 pregnant women) were included in the meta-analysis. mHealth interventions significantly improved total physical activity (TPA) (SMD = 0.44, 95% CI: 0.31 to 0.57, <i>P</i> &lt; 0.00001, I² = 0%) and also demonstrated a small but significant improvement in moderate-to-vigorous physical activity (MVPA) (SMD = 0.21, 95% CI: 0.03 to 0.40, <i>P</i> = 0.03, I² = 36%). Prespecified subgroup analysis revealed that the gestational week at the start of the intervention was a key factor influencing the effect on MVPA, with interventions initiated in early pregnancy (≤ 14 weeks) showing significantly better outcomes than those started later. In contrast, the effect on TPA was robust across all subgroups.</p> Conclusion <p>mHealth interventions effectively promote physical activity in pregnant women, yielding a moderate and robust improvement in total physical activity and a small but significant increase in MVPA. The findings suggest that initiating interventions in early pregnancy (≤ 14 weeks) may be more effective for promoting MVPA. These findings provide evidence-based support for integrating mHealth strategies into routine antenatal care to promote physical activity.</p> Systematic review registration <p>This systematic review and meta-analysis has been registered with PROSPERO (<a href="https://www.crd.york.ac.uk/prospero">www.crd.york.ac.uk/prospero</a>), identifier CRD420251107861.</p>