Objectiveto examine the effects of supervised group exercise on maternal psychological outcomes and commonly reported pregnancy complaints. Designan observer-blinded randomized controlled trial. SettingNorwegian School of Sport Sciences, Oslo, Norway. Participants105 sedentary, nulliparous pregnant women, mean age 30.7(±4.0) years, pre-pregnancy BMI 23.8 (±4.3), were assigned to either exercise (n=52) or control group (n= 53) at mean gestation week 17.7 (±4.2). Interventionthe exercise intervention followed ACOG guidelines and included a 60 minutes general fitness class, with 40 minutes of endurance training/aerobic and 20 minutes of strength training and stretching/relaxation, performed at least twice per week for a minimum of 12 weeks. Measurementsoutcome measures were assessed through standardized interviews pre- and post-intervention (gestation week 36.6, ±0.9), and included psychological variables related to quality of life, well-being, body image and pregnancy depression, as well as assessment of 13 commonly reported pregnancy complaints. Findingspost-intervention, using intention to treat (ITT) analysis, women randomized to exercise rated their health significantly better compared to women in the control group (p=0.02) and reported less fatigue related to everyday activities (p=0.04). Women with complete exercise adherence (≥24 sessions) had significantly better scores on measurements of feelings related to sadness, hopelessness and anxiety (p<0.01), compared to the control group. Contradictory, the control group reported higher life enjoyment (p<0.01). There were no significant group differences in body-image or pregnancy depression. With respect to analysing pregnancy complaints according to ITT, no differences between the groups were found. A comparison of the women who attended ≥19 (80%, n=21) or ≥24 (100%, n=14) exercise sessions with the control-participants, showed that fewer women in the exercise group reported nausea/vomiting and numbness/poor circulation in legs. Key conclusion and implication for practiseparticipation in regular group exercise during pregnancy contributed to improvements in some variables related to maternal well-being and quality of life. Women with high exercise adherence had significantly better results on several health variables reaping the highest benefits. A qualitative study exploring the barriers of women in achieving recommended amount of activity may be necessary to understand this population and developing better clinical practice educational tools.