Neuraxial analgesia has shown to be the gold standard for effective labor pain relief, offering numerous benefits including enhanced pain control and maternal satisfaction. The methods to achieve neuraxial analgesia include lumbar epidural (LE), and combined spinal epidural (CSE). While LE may not consistently provide optimal pain relief, leading to frequent maternal requests for supplemental analgesics, CSE presents a promising advancement. This is due to the rapid onset of pain relief from intrathecal components, complemented by the longer-lasting effects of epidural medications. Intrathecal drugs have demonstrated the ability to offer more symmetrical blockades compared to epidurally administered medications. Nonetheless, some clinicians remain cautious about CSE due to the potential for increased pain when transitioning from spinal to less effective epidural analgesia. Long-acting opioids like morphine in the intrathecal space may mitigate this problem by providing transitional analgesia to the laboring parturient.

The primary aim of this randomized controlled trial is to provide evidence of whether the addition of 100 mcg of morphine in the intrathecal (spinal) component of CSE reduces the rate of breakthrough pain during labor.

The addition of morphine to a combination of bupivacaine and lipophilic opioids (fentanyl) for the spinal component of CSE for labor analgesia has been shown to increase the duration of analgesia. A meta-analysis by Al-Kazwini and coworkers suggests a possible beneficial prolonging effect of adding morphine to spinal analgesia, however, the authors concluded that more adequately powered randomized controlled trials (RCTs) are required to determine the benefits and harms of intrathecal morphine (ITM).

This prolonged duration of action of ITM may reduce the need for frequent top-ups, which could alleviate nursing and anesthesiologist workload and enhance maternal satisfaction. An RCT conducted by Vasudevan and coworkers has concluded that the addition of 100 mcg ITM along with bupivacaine and fentanyl reduced the incidence of breakthrough pain in labor. Another dose-finding study comparing 50 and 100 mcg of ITM as a component of CSE labor analgesia concluded that 100 mcg of ITM significantly lowers the local anesthetic consumption and shorter duration of the first stage of labor without any significant difference in adverse effects. The RCT by Vasudevan et al. had a small sample size, enrolled mixed parity patients, and utilized continuous infusion for labor analgesia maintenance.

Hence, the investigators plan to conduct adequately powered RCT enrolling only primigravidae patients, which tend to have more prolonged labor than multiparous and programmed intermittent epidural bolus (PIEB) with patient-controlled epidural analgesia (PCEA) will be used, which is a more contemporary labor maintenance technique.

Inclusion Criteria:

• Adult (≥18 years) term primiparous (≥37 weeks) patients with live singleton pregnancy
• Patients who request labour analgesia and do not have any contraindications for neuraxial analgesia.
• Less than or equal to 6 cm cervical dilation during the last vaginal examination.

Exclusion Criteria:

• Patients who are expected to be discharged within 24 hours of delivery.
• Patients with chronic pain conditions, opioid use disorder, pre-gestational diabetes, obstructive sleep apnea, morbid obesity (BMI >40 kg/m2), or fetal abnormalities.
• Patients who have intramuscular morphine within 12 hours or fentanyl >200 mcg in the preceding 4 hours.
• Participants will be excluded from further analysis in case of spinal analgesic failure
• Participants will be excluded from further analysis if labour lasts less than 2 hours