Effect of Dural Puncture Epidural Analgesia on Oxytocin in Early vs Late Labor

Oxytocin is a key hormone that regulates uterine contractions during labor. Dural Puncture Epidural Analgesia (DPEA) is a modern technique for labor pain relief that provides faster onset and more reliable analgesia than standard epidural.While it is known that neuraxial analgesia can suppress oxytocin levels, it is unclear whether this effect depends on the stage of labor at which analgesia is administered. This prospective comparative study will enroll 120 pregnant women in spontaneous labor who request DPEA, divided into two groups: Early group (cervical dilation≤5 cm, n=60) and Late group (cervical dilation≥6 cm , n=60). Both groups receive identical DPEA (a total volume of 15 mL containing 0.1% bupivacaine and 100 µg fentanyl is administered through the epidural catheter, following dural puncture with a 26G spinal needle without intrathecal drug injection). The primary outcome is the percentage change in plasma oxytocin from baseline (T-0, before analgesia) to T-Eff (30 minutes after onset of effective analgesia defined as VAS\

Inclusion Criteria: * Gestational age 37-41 weeks, singleton pregnancy, vertex presentation * Spontaneous onset of labor (not induced) * Request for neuraxial labor analgesia (DPEA) * Cervical dilation ≤5 cm (Early Group) or ≥ 6 cm (Late Group) at the time of DPEA * Age 18-40 years, ASA physical status II * Able to communicate in Turkish; written informed consent Exclusion Criteria: CRITICAL EXCLUSION (methodological requirement): * Any administration of exogenous oxytocin (induction or augmentation) prior to T-0 blood sampling * Use of misoprostol, dinoprostone, or other labor-stimulating agents STANDARD EXCLUSION: * Opioid use within the preceding 12 hours * Membrane rupture \>2 hours before enrollment * Uterine hyperstimulation * History of lumbar spine surgery, coagulopathy (platelet count \2 attempts, failed dural puncture confirmation)