Effects of OPRM1 A118G polymorphism on epidural analgesia with fentanyl during labor: a meta-analysis

Emerging evidence has shown that the most common polymorphism (A118G; rs1799971 A>G) in the μ-opioid receptor (OPRM1) gene may influence the response to labor analgesia, but individually published studies showed inconclusive results. This meta-analysis aimed to derive a more precise estimation of the effects of the OPRM1 A118G polymorphism on epidural analgesia with fentanyl during labor. A literature search was conducted on PubMed, Embase, Web of Science, and China BioMedicine databases before April 1st, 2013. The crude standardized mean difference (SMD) or odds ratio (OR) with 95% confidence interval (CI) was calculated. Six clinical studies were included with a total 838 women who received epidural analgesia with fentanyl during labor. The meta-analysis results indicated that women carrying the G allele (AG+GG) of the OPRM1 A118G polymorphism required less fentanyl doses to achieve adequate pain relief compared with those with the AA homozygote (SMD=-0.24, 95% CI [-0.44, -0.03], p=0.022). The 118G variant was associated with a decreased ED50 of fentanyl for labor analgesia (SMD=-1.56, 95% CI [-1.97, -1.15], p