Study design
ABNORMAL PREGNANCY, RECRUITMENT, PREGNANCY COMPLICATIONS
A randomized controlled trial was conducted in this study. Women at the gestational age of 30–31 weeks who received regular prenatal examinations in the obstetrics clinic of a first-class tertiary general hospital in Hainan Province, China, from July 2020 to December 2020 were informed about the recruitment. A total of 458 showed the interest. After screening and communication, 314 subjects were excluded, including 148 multiparas, 35 women with pregnancy comorbidities, 79 women with pregnancy complications and 52 women with a history of abnormal pregnancy. Finally, 144 pregnant women at the gestational age of 30–31 weeks were enrolled in this study (see Fig. 
Comparison of the sociodemographic data between the intervention and control groups (N = 144)
Flowchart of the study