Materials and Methods: This study was a randomized clinical trial. A total of 178 participants were selected based on the specific selection criteria and randomly allocated to control and intervention groups. The women in the intervention group were asked to join a planned exercise with the birth ball including a 20-minute well-defined exercise three times a week for 6?8 weeks at home whereas those in the control group followed up the routine prenatal cares. The questionnaires were completed by the participants at the four and eight-centimeter cervical dilations.

Results: Based on the results, birth ball exercises could significantly improve childbirth self-efficacy and pain so that labour pain was lower in this group of women as compared to the other group (P < 0.001 in both cervical dilatations). In addition, the score of self-efficacy was higher in the intervention group compared to the control group (P < 0.001). Further, the result of generalized estimating equation model showed that birth ball exercise can decrease the childbirth pain. However, part of this effect may be related to an increase in the patients? self-efficacy (30%-40%).

Conclusions: In general, although birth ball exercise could decrease the childbirth pain, part of this effect was probably associated with an increase in self-efficacy of the patients.