The increased prevalence of obesity has led to major health care issues in obstetric practice. Nevertheless, despite a major international effort, there is little evidence for interventions which can improve clinical outcome. Two reports from the LIMIT randomised controlled trial of more than 2,000 overweight and obese women, recently reported in BMC Medicine, show how a lifestyle intervention in Australian women changes dietary and physical activity behaviours without any evidence of harm to the health of the newborn infant and with some suggestion of benefit. The improvements in maternal lifestyle, albeit modest, may account for a previously reported reduction in the number of macrosomic infants born to LIMIT participants randomised to the intervention arm of the trial. Please see related articles: http://www.biomedcentral.com/1741-7015/12/161 and http://www.biomedcentral.com/1741-7015/12/163.