3.1 \| Study design In this study, a single-blinded, randomized, controlled trial with a prospective pretest-posttest experimental design was implemented to examine the effects of low-impact aerobic exercise with modified yoga movements on sleep quality and maternal-fetal attachment in pregnant women.

3.2 \| Participants Participants for this study were recruited from the prenatal clinic of a medical center in southern Taiwan. A sample size of 63 per group was considered sufficient to estimate a medium effect of .50 with α-value of 0.05 and a power of 0.08 (Polit \& Beck, 2011). Considering a 20% attrition rate over 3 months, 140 pregnant women were enrolled.

3.3 \| Intervention The intervention group received a DVD with low-impact aerobic exercises developed by the researchers in collaboration with a qualified prenatal yoga teacher. The program incorporated modified yoga movements suitable for pregnant women. The DVD provides an illustration with the written caption, "Please take enough water before exercise, and wear loose and comfortable clothes in a suitable environment. If you feel tired, stop exercising immediately." The DVD's narrator then says, "Now you are ready to prepare a comfortable, solid chair with a chair back." With a soft musical background, the exercise actions were arranged in following order: warm-up → neck → shoulder → arm → chest → waist →leg → regulating the breathing. The first 14.5 minutes of the yoga exercises were performed in a sitting position, followed by 3.5 minutes in standing position, and then returning to 2 minutes in sitting position. The exercises were developed as a progressive program in order to achieve the goals of strength-conditioning, moderate-intensity exercise (ACOG, 2015). The yoga teacher instructed the participants to touch their heart with their right hand and their abdomen with their left hand, feeling a connection with the fetus in the warm-up and in the final breath-regulating stage of exercise (2 minutes). An expert video producer edited the DVD for sound, animation, and subtitles. The exercise program requires twenty minutes to complete. Women were instructed to use the DVD 3 times a week for 3 months. The DVD was reviewed for content validity by two clinical obstetric nursing experts, and in addition, two pregnant women in their second trimester reviewed the DVD for face validity.

3.5 \| Procedure and ethical considerations The present study was carried out from January to October 2014 after approval was obtained from the institutional review board of the participating institution. One hundred and forty women who met the inclusion criteria and returned their consent documents were systematically assigned, from a random starting point to experimental (n = 70) or a control (n = 70) group. Women usually talk to each other during the prenatal check and this could cause study data contamination, so we used a month as the unit of allocation to avoid between-group data contamination. The first month collecting data was control group decided by drawing lots (two lots which were marked "E" for experimental group and marked "C" for control group in a sack). Research assistant drew the lot from the sack. Then, the following month, group allotment was systematically assigned in sequence to either the experimental group or the control group.

In addition to routine care, the experimental group was given the DVD and instructed to engage in the aerobic exercise program shown on the DVD. The control group received routine prenatal care only. The two groups were asked to complete the demographic data form, the MMFAS, and the PSQI at 3 time periods: before the intervention, at 4 weeks, and 12 weeks post-intervention. All participants in both groups received a small gift after completing the pretests. The latter two sets of questionnaires were mailed with postage-paid, pre-addressed envelopes to all of the participants for them to complete and return. Sixty-one participants in the experimental group and 62 participants in the control group completed the 1-month posttests; 51 participants in the experimental group and 47 participants in control group completed the 3-month posttests. The CONSORT diagram of this study is shown in Figure 1. The experimental group participants were asked to complete an open-ended question on the subjective benefits of practicing aerobic exercise.

3.6 \| Data analysis Tests for differences in baseline characteristics between the two groups included the χ2 test for categorical variables and the t-test for continuous variables. The effectiveness of yoga-based low-impact aerobic exercise on maternal-infant attachment and sleep quality was determined by a paired t-test. All results with p \< .05 were considered statistically significant. The SPSS (version 17.0 for Windows, SPSS Inc., Chicago, IL, USA) statistical software package was used to analyze the data.