Effect of a Vertical Birthing Chair on Labor

This prospective, randomized, controlled, parallel-group clinical trial will investigate the effects of using a vertical birthing chair during the active second stage of labor on fetal head descent and rotation, as objectively assessed by intrapartum ultrasonography. The study will also evaluate the effects of maternal position on the progression of labor, mode of delivery, maternal obstetric outcomes, childbirth experience, and neonatal outcomes.

The sample size was calculated using G*Power based on the expected between-group difference in the change in the Angle of Progression (AoP), the primary outcome of the study. Assuming a moderate effect size (Cohen's d = 0.50), a two-sided type I error rate of 5% (α = 0.05), and 80% statistical power, at least 64 participants will be required in each group. To account for an anticipated attrition or protocol-deviation rate of approximately 10%, 72 participants will be enrolled in each group, resulting in a total planned sample size of 144 participants.

At the beginning of the active second stage of labor, participants will be randomly assigned in a 1:1 ratio to either the vertical birthing chair group or the standard semi-recumbent position group. Computer-generated block randomization will be used to maintain balanced group sizes throughout recruitment. The randomization sequence will be prepared by an investigator who is independent of participant recruitment and clinical assessment. Allocation concealment will be ensured using sequentially numbered, opaque, sealed envelopes. Group allocation will be revealed only after the baseline intrapartum ultrasonographic assessment has been completed.

Participants allocated to the intervention group will be positioned on a vertical birthing chair after full cervical dilatation. The maternal trunk will be maintained at an inclination of approximately 60-90 degrees, with the feet adequately supported. Participants will be allowed to move within safe limits during labor. A change in position will be permitted when clinically required for maternal or fetal reasons and will be documented as a protocol deviation or crossover, as appropriate.

Participants allocated to the control group will be managed on a delivery bed in the standard semi-recumbent position, with the maternal trunk elevated approximately 30-45 degrees. In both groups, labor management will otherwise follow the hospital's routine obstetric practices. Fetal monitoring, oxytocin administration, analgesia, and any necessary obstetric interventions will be provided according to clinical indications. Decisions regarding operative vaginal delivery, cesarean delivery, episiotomy, or other interventions will be made by the attending clinical team based on maternal and fetal conditions.

All intrapartum ultrasonographic examinations will be performed by the same obstetrician experienced in intrapartum ultrasound to reduce interobserver variability. Fetal head position will be evaluated by transabdominal ultrasonography, whereas fetal head descent will be assessed by transperineal ultrasonography.

The following intrapartum ultrasonographic parameters will be recorded:

Angle of Progression (AoP) Head-Perineum Distance (HPD) Head-Symphysis Distance (HSD) Fetal head position, classified as occiput anterior, occiput transverse, or occiput posterior Fetal head rotation Presence of caput succedaneum Presence of molding

Ultrasonographic assessments will be performed at four predefined time points:

T0: At full cervical dilatation and before randomization T1: Fifteen minutes after initiation of the assigned maternal position T2: Thirty minutes after initiation of the assigned maternal position T3: Immediately before birth or when a decision for operative delivery is made

Each ultrasonographic parameter will be measured twice at each assessment, and the mean of the two measurements will be used in the statistical analyses. The principal ultrasonographic evaluation will focus on the change in AoP over time and the difference in this change between the intervention and control groups. Changes in HPD, HSD, and fetal head position or rotation will provide additional objective information regarding fetal head descent and rotational progress.

Participants' sociodemographic and obstetric characteristics will be recorded using a standardized case report form. These data will include maternal age, height, body weight, pre-pregnancy body mass index, gestational age at delivery, spontaneous or induced onset of labor, epidural analgesia, and oxytocin use.

Clinical labor and delivery data will include the duration of the active second stage, total duration of the second stage, mode of delivery, requirement for operative vaginal delivery, cesarean delivery, episiotomy, degree of perineal laceration, postpartum blood loss, and need for additional uterotonic medication.

Maternal childbirth experience will be assessed within the first 24 hours after birth using the validated Turkish version of the Childbirth Experience Questionnaire (CEQ). The questionnaire evaluates four dimensions of childbirth experience: Own Capacity, Professional Support, Perceived Safety, and Participation. Scores will be calculated for each domain and for the overall questionnaire, with higher scores indicating a more positive childbirth experience.

Neonatal assessments will include birth weight, Apgar scores at 1 and 5 minutes, umbilical artery pH, umbilical artery base deficit, and admission to the neonatal intensive care unit.

Study data will be entered into standardized case report forms and checked for completeness, accuracy, acceptable ranges, and internal consistency. Ultrasonographic findings and clinical outcomes will be verified against ultrasound records, labor monitoring documentation, and maternal and neonatal medical records. Missing, unavailable, uninterpretable, or out-of-range data will be identified and documented before analysis. Reasons for withdrawal, crossover, incomplete ultrasonographic assessment, or deviation from the assigned position will also be recorded.

The statistical analysis will follow a prespecified statistical analysis plan. Baseline characteristics will be summarized by randomized group. Repeated ultrasonographic measurements will be analyzed to assess changes over time and differences in these changes between the two groups. Maternal and neonatal outcomes will also be compared between the intervention and control groups using statistical methods appropriate to the distribution and measurement level of each variable. The principal analysis will be conducted according to the intention-to-treat principle; an additional per-protocol analysis may be performed to evaluate the findings among participants who remain in their assigned position according to the study protocol. Effect estimates will be reported with 95% confidence intervals, and a two-sided p value of <0.05 will be considered statistically significant.