*2.3. Participants and Sample Size*

Participants were recruited from May to October 2021 at the prenatal clinic of the University Public Hospital Federico II of Naples, which is also an obstetric emergency department.

All pregnant women, aged between 18 and 40 years, with a low-risk full-term pregnancy (between the 37th and 42nd week of amenorrhea) undergoing labor and with the fetus in cephalic presentation were included in the study. Pregnant women with maternal and/or fetal pathologies, subjected to drug induction to labor, or who had resorted to epidural analgesia, were excluded from the study.

A statistical power analysis was performed for sample size estimation through G\*Power program (Heinrich Heine University, Düsseldorf, Germany). Based on parameters used by Tanvisut et al. [28], the effect size was set at 0.05, the *α* at 0.05 (two-tailed), and the power at 90%. Results indicated that a sample size of at least 42 participants for each group was needed.

During the study period, 1258 women were admitted to the delivery room at the hospital. Among them, a total of 96 women met the inclusion criteria. They were randomly assigned to either the intervention group (*n* = 48) or control group (*n* = 48). Four women for each group were then excluded because they needed to take drugs to induce labor or to undergo epidural analgesia. Thus, analyses were conducted on 44 women in the experimental group and 44 in the control group. The CONSORT flow diagram is shown in Figure 1.
