Effect of a Vertical Birthing Chair on Labor

The goal of this randomized clinical trial is to evaluate whether the use of a vertical birthing chair during the active second stage of labor improves fetal head descent and rotation. The effects will be assessed objectively by intrapartum ultrasonography, and effects on labor progress and maternal and neonatal outcomes. The main questions it aims to answer are: * Does the use of a vertical birthing chair improve intrapartum ultrasonographic parameters of fetal head descent and rotation compared with the standard semi-recumbent position? * Does the use of a vertical birthing chair affect the duration of the second stage of labor, mode of delivery, perineal injury, postpartum blood loss, maternal childbirth experience, and neonatal outcomes? Researchers will compare women assigned to use a vertical birthing chair with women assigned to the standard semi-recumbent position to determine the effects of maternal position during the active second stage of labor. Participants will: * Be randomly assigned to either the vertical birthing chair group or the standard semi-recumbent position group during the active second stage of labor. * Undergo intrapartum ultrasonographic assessment of fetal head descent and rotation. * Be evaluated for the duration and mode of delivery, episiotomy and perineal trauma, postpartum blood loss, and neonatal outcomes. * Complete the Childbirth Experience Questionnaire (CEQ) to assess their childbirth experience.

Inclusion Criteria: * Pregnant individuals aged 18-40 years * Gestational age between 37 weeks 0 days and 41 weeks 0 days * Singleton, live fetus * Cephalic fetal presentation * Planned vaginal delivery * Spontaneous or induced labor * Full cervical dilatation at the time of randomization * Stable maternal and fetal clinical status * Provision of written informed consent to participate in the study Exclusion Criteria: * History of previous cesarean delivery or other uterine surgery * Multiple pregnancy * Breech, transverse, or other non-cephalic fetal presentation * Placenta previa or vasa previa * Intrauterine fetal death * Known or suspected major fetal anomaly * Development of an indication for emergency cesarean delivery before randomization * Severe preeclampsia or eclampsia * Orthopedic or neurological condition that prevents or makes the use of a vertical birthing position unsafe * Withdrawal of consent or unwillingness to participate