The A118G single-nucleotide polymorphism of human μ-opioid receptor gene and use of labor analgesia.
The human µ-opioid receptor (MOR) is the major site of action of endogenous opioids and most of the clinically used opioid analgesics. The single-nucleotide polymorphism (SNP), A118G of the MOR 1 gene (OPRM1), has been associated with altered pain perception. The aim of this study was to investigate whether this polymorphism of OPRM1 is associated with a number of pain-related behaviors during labor. In this observational retrospective population-based study, pregnant women (n = 814) were recruited at gestational week 18. A plasma sample was collected from each participant and an SNP genotyping assay was performed. No differences in sociodemographic variables or labor pain-related outcomes, such as stage of cervical dilation on arrival at the delivery unit or use of any type of second-line analgesia during spontaneous labor, were found between noncarriers and G-allele carriers of OPRM1. We conclude that there is no association between the A118G polymorphism of OPRM1 regarding pain-related behavior during labor.