Main findings
In this large RCT, the intention-to-treat analysis showed no effect of a supervised 12 weeks group exercise intervention on psychological well-being measured by the WHO-5 at gestational weeks 29–34 (primary outcome). Perprotocol analysis of women who attended ≥75% of the exercise sessions showed a statistically significant higher WHO-5 mean relative to controls at gestational weeks 29–34. Intriguingly, eight weeks postpartum, women in the intervention group had a statistically significant higher mean WHO-5 than women in the control group.