Interleukin-1 receptor antagonist, mode of analgesia and risk of Caesarean delivery after onset of labour: a Mendelian randomisation analysis

BACKGROUND: Lower circulating levels of the anti-inflammatory cytokine interleukin-1 receptor antagonist (IL-1ra) are associated with intrapartum inflammation and epidural analgesia-related maternal fever, both of which increase the rate of obstetric interventions. We hypothesised that genetic variants determining IL-1ra levels would be associated with Caesarean delivery rates after the onset of labour. METHODS: We performed Mendelian randomisation analyses in parous women ≥16 yr old who received either non-neuraxial or neuraxial analgesia for their first two labours (UK Biobank). We used an established genetic score (calculated as 0-4, determined by the presence/absence of rs6743376 and rs1542176 alleles), in which the complete absence of both alleles causes the lowest IL-1ra levels. The primary outcome was Caesarean delivery after the onset of labour (odds ratio [OR]: 95% confidence intervals). RESULTS: There were 7731 women (mean [standard deviation] age at first birth: 25 [5] yr) who had complete genetic scores and delivery data. For women who received non-neuraxial analgesia, Caesarean delivery rates were different across allele scores (χ2=12.4; P=0.015): 104/596 (17.4%) women with zero allele score underwent Caesarean delivery, compared with 654/5015 (13.0%) with allele score ≥1 (OR 1.41; 1.12-1.77). For women who had neuraxial analgesia, Caesarean delivery was not different across allele scores, ranging from 18.1% to 20.8% (χ2=0.29; P=0.99). Caesarean delivery was independent of type of analgesia for 818/7731 (10.6%) women with zero allele scores (OR 0.93; 0.63-1.39), but was higher in women receiving neuraxial analgesia with allele scores ≥1 (OR 1.55; 1.35-1.79; P<0.001). CONCLUSIONS: Mendelian randomisation analysis suggests that higher IL-1ra levels are associated with reduced Caesarean delivery rate. Neuraxial analgesia appears to disrupt this link. CLINICAL TRIAL REGISTRATION: UK Biobank study 62745

IL-1ra polymorphisms and risk of epidural-related maternal fever (EPIFEVER-2): study protocol for a multicentre, observational mechanistic cohort study

Background: Laboratory data suggest that insufficient circulating levels of the anti-inflammatory cytokine interleukin-1 receptor antagonist (IL-1ra) are associated with intrapartum inflammation and epidural-related maternal fever, both of which increase the rate of obstetric interventions and antibiotic use during labour. Genetic polymorphisms strongly influence IL-1ra levels in the general population. We aim to examine the association between IL-1ra polymorphisms and epidural-related maternal fever using Mendelian randomization analysis. Methods: EPIFEVER-2 is a multicentre UK trial enrolling 637 women receiving epidural analgesia for labour. Blood samples obtained no later than four hours after epidural insertion will provide deoxyribonucleic acid for Taqman single-nucleotide polymorphism genotyping for presence/absence of rs6743376, rs1542176 alleles for IL-1ra, to establish the genetic score. The absence of both alleles is associated with the lowest IL-1ra levels. The primary outcome is pyrexia (>38°C) or intrapartum antibiotic administration. Secondary outcomes include mode of delivery, maternal and neonatal healthcare interventions. Results: The EPIFEVER-2 study was prospectively registered (ISRCTN99641204) following ethical approval. Participant recruitment began in May 2021, with 221 women recruited across three centres as of November 21, 2021. Conclusions: EPIFEVER-2 will generate the largest prospective dataset detailing the incidence and consequences of epidural-related maternal fever. Using Mendelian randomisation analysis, a causative role for lower IL1-ra levels in determining the risk of epidural-related maternal fever and/or antibiotic administration before delivery will be examined

IL-1ra polymorphisms and risk of epidural-related maternal fever (EPIFEVER-2): study protocol for a multicentre, observational mechanistic cohort study.

BACKGROUND: Laboratory data suggest that insufficient circulating levels of the anti-inflammatory cytokine interleukin-1 receptor antagonist (IL-1ra) are associated with intrapartum inflammation and epidural-related maternal fever, both of which increase the rate of obstetric interventions and antibiotic use during labour. Genetic polymorphisms strongly influence IL-1ra levels in the general population. We aim to examine the association between IL-1ra polymorphisms and epidural-related maternal fever using Mendelian randomization analysis. METHODS: EPIFEVER-2 is a multicentre UK trial enrolling 637 women receiving epidural analgesia for labour. Blood samples obtained no later than four hours after epidural insertion will provide deoxyribonucleic acid for Taqman single-nucleotide polymorphism genotyping for presence/absence of rs6743376, rs1542176 alleles for IL-1ra, to establish the genetic score. The absence of both alleles is associated with the lowest IL-1ra levels. The primary outcome is pyrexia (>38°C) or intrapartum antibiotic administration. Secondary outcomes include mode of delivery, maternal and neonatal healthcare interventions. RESULTS: The EPIFEVER-2 study was prospectively registered (ISRCTN99641204) following ethical approval. Participant recruitment began in May 2021, with 221 women recruited across three centres as of November 21, 2021. CONCLUSIONS: EPIFEVER-2 will generate the largest prospective dataset detailing the incidence and consequences of epidural-related maternal fever. Using Mendelian randomisation analysis, a causative role for lower IL1-ra levels in determining the risk of epidural-related maternal fever and/or antibiotic administration before delivery will be examined