Sample size
pain
The women were selected from the patients referring to the maternity ward of the hospital using the convenience sampling method. Afterward, women were assigned into three groups, namely infrared belt, hot water bag, and control (routine care), using the block randomization method. To determine the sample size, the results of the pilot study were applied on ten women in three group, and the formula of comparing two means was used to estimate the pain score. The sample size of at least 45 women in each group was calculated, in which the final sample size was determined at 50 women in three groups based on 80% test power, 95% confidence interval, 5% maximum margin of error, and 10% drop-out rate. It should be mention that the results of the pilot study were not used in the final analysis.