Abstract: We included four randomised controlled trials involving 1933 participants. For the primary outcome category of health, there was moderate quality evidence from one study that women who received prenatal support via mobile phone messages had significantly higher satisfaction than those who did not receive the messages, both in the antenatal period (mean difference (MD) 1.25, 95% confidence interval (CI) 0.78 to 1.72) and perinatal period (MD 1.19, 95% CI 0.37 to 2.01). Their confidence level was also higher (MD 1.12, 95% CI 0.51 to 1.73) and anxiety level was lower (MD -2.15, 95% CI -3.42 to -0.88) than in the control group in the antenatal period. In this study, no further differences were observed between groups in the perinatal period. There was low quality evidence that the mobile phone messaging intervention did not affect pregnancy outcomes (gestational age at birth, infant birth weight, preterm delivery and route of delivery). For the primary outcome category of health behaviour, there was moderate quality evidence from one study that mobile phone message reminders to take vitamin C for preventive reasons resulted in higher adherence (risk ratio (RR) 1.41, 95% CI 1.14 to 1.74). There was high quality evidence from another study that participants receiving mobile phone messaging support had a significantly higher likelihood of quitting smoking than those in a control group at 6 weeks (RR 2.20, 95% CI 1.79 to 2.70) and at 12 weeks follow-up (RR 1.55, 95% CI 1.30 to 1.84). At 26 weeks, there was only a significant difference between groups if, for participants with missing data, the last known value was carried forward. There was very low quality evidence from one study that mobile phone messaging interventions for self-monitoring of healthy behaviours related to childhood weight control did not have a statistically significant effect on physical activity, consumption of sugar-sweetened beverages or screen time. For the secondary outcome of acceptability, there was very low quality evidence from one study that user evaluation of the intervention was similar between groups. There was moderate quality evidence from one study of no difference in adverse effects of the intervention, measured as rates of pain in the thumb or finger joints, and car crash rates. None of the studies reported the secondary outcomes of health service utilisation or costs of the intervention. We found very limited evidence that in certain cases mobile phone messaging interventions may support preventive health care, to improve health status and health behaviour outcomes. However, because of the low number of participants in three of the included studies, combined with study limitations of risk of bias and lack of demonstrated causality, the evidence for these effects is of low to moderate quality. The evidence is of high quality only for interventions aimed at smoking cessation. Furthermore, there are significant information gaps regarding the long-term effects, risks and limitations of, and user satisfaction with, such interventions.

Plain-language summary: There was moderate quality evidence from one study which showed that pregnant women who received supportive, informative text messages experienced higher satisfaction and confidence, and lower anxiety levels in the antenatal period than women who did not receive these. There was low quality evidence that there was no difference in pregnancy outcomes. We found one trial that provided high quality evidence that regular support messages sent by text message can help people to quit smoking, at least in the short-term. One study assessing whether mobile phone messaging promoted use of preventive medication reported moderate quality evidence of higher self-reported adherence by people receiving the messages. A fourth study on healthy behaviours in children found very low quality evidence showing that the interventions had no effect. There was very low quality evidence from one study that people's evaluation of the intervention was similar between groups. There was moderate quality evidence from one study of no difference in harms of the intervention, measured as rates of pain in the thumb or finger joints, and car crash rates. There were no studies reporting outcomes related to health service utilisation or costs. Although we find that, overall, mobile phone messaging can be helpful for some aspects of preventive health care, much is not yet known about the long-term effects or potential negative consequences.