Maternal Salivary Glutamate in Women Undergoing Vaginal Delivery: A Comparison Between Epidural Labor Analgesia and Systemic Morphine Analgesia

Introduction: Labor pain is among the most intense forms of acute pain, mediated in part by excitatory glutamatergic neurotransmission within central nociceptive pathways. Glutamate plays a key role in spinal dorsal horn signaling and central sensitization, yet its peripheral dynamics during labor and in response to different analgesic modalities remain unclear. This exploratory study aimed to evaluate whether maternal salivary glutamate levels differ between epidural labor analgesia and systemic morphine analgesia during normal vaginal delivery. Method: In this observational comparative study, 36 women were selected to either epidural analgesia (n = 16) or systemic morphine analgesia (n = 20). Salivary samples were collected during active labor and analyzed for glutamate concentration using a validated enzymatic colorimetric assay. Clinical and demographic data were recorded. Non-parametric tests were applied due to non-normal distribution of glutamate levels. Results: Baseline maternal and perinatal characteristics were comparable between groups. Median salivary glutamate levels were higher in the epidural group than in the morphine group (5.32 nmol/µL [IQR 2.83–8.00] vs. 3.99 nmol/µL [IQR 2.26–8.03]), but the difference was not statistically significant (p = 0.599). Glutamate concentrations showed marked inter-individual variability (0.14–29.89 nmol/µL) and a right-skewed distribution. No significant associations were observed between glutamate levels and maternal age, Body Mass Index, gestational age, birth weight, or obstetric comorbidities. Conclusion: In this exploratory cohort, maternal salivary glutamate concentrations did not differ significantly between epidural labor analgesia and systemic morphine analgesia during labor. The variability observed suggests complex and heterogeneous regulation of peripheral glutamatergic activity in parturition. Further larger-scale studies integrating central and peripheral measurements are warranted.