Trial participants
From August 2016–September 2018, 714 pregnant women were assessed for eligibility. A total of 67 women did not receive information about the study and 647 were initially invited to participate. A total of 282 women were randomly assigned to either supervised group exercise (n=143) or the control group (n=139) (Figure 1). Eight women from the intervention group withdrew consent: one found the exercise uncomfortable to perform, two preferred other kinds of physical activity and five women could not find the time to participate.
Baseline maternal characteristics in the intervention group and the control group were comparable (Table 1).
The study population´s mean age was 31.8 years (SD 3.9), 73.4% were nulliparous, the mean pre-pregnancy body mass index was 22.8 kg/m2 (SD 3.5), 87% had a higher education or advanced degree, 99% did not smoke at baseline and 78% of the study population were physically active ≥3.5 hours a week before pregnancy. The median weekly amount of physical activity was measured after the intervention and eight weeks postpartum: 4 hours (min 0–max 24) in the intervention group and 4 hours (min 0–max 16) in the control group at 29–34 weeks of gestation, 6 hours (min 0–max 25) in the intervention group and 6 hours (min 0–max 25) in the control group eight weeks postpartum.
A total of 127 (95%) participants in the intervention group and 118 (86%) in the control group responded to the self-administered questionnaire at 29–34 weeks of gestation, while 99 (74%) participants in the intervention group and 84 (61%) in the control group responded eight weeks postpartum (Figure 1).