Factors associated with infection following operative vaginal birth - a secondary analysis of the ANODE randomized controlled trial.
Humphreys ABC., Linsell L., Knight M.
BACKGROUND: The recent ANODE randomized controlled trial showed that women allocated prophylactic intravenous amoxicillin and clavulanic acid had a significantly lower risk of developing confirmed or suspected infection within 6 weeks of operative vaginal birth. Some international and national guidelines have subsequently been updated to include prophylactic antibiotics after operative vaginal birth. However, the generalizability of the ANODE results may be limited in settings where episiotomy rate is lower (89% of women in ANODE had an episiotomy). Additionally, there was a high burden of infection in ANODE despite prophylactic antibiotic. It is essential to identify modifiable risk factors for infection after operative vaginal birth including timing of antibiotic administration. BACKGROUND OBJECTIVES: This study aimed to evaluate if the effectiveness of the prophylactic antibiotic in reducing confirmed or suspected infection was independent of perineal trauma, identify risk factors for infection after operative vaginal birth and investigate variation in efficacy with timing of antibiotic administration. STUDY DESIGN: This study was a secondary analysis of 3225 women with primary outcome data from the ANODE randomized controlled trial.Women were divided into subgroups according to the perineal trauma experienced (episiotomy and/or perineal tear). The consistency of the prophylactic antibiotics in preventing infection across the subgroups was assessed using log binomial regression and the likelihood ratio test.Multivariable log binomial regression was used to investigate factors associated with infection. The multivariable risk factor model was subsequently fitted to the group of women who received amoxicillin and clavulanic acid to investigate the timing of antibiotic administration. RESULTS: Of the 3225 included in the secondary analysis, 2144 (66.5%) had an episiotomy alone, 726 (22.5%) had an episiotomy and a tear, 277 (8.6%) had a tear alone and 78 (2.4%) had neither episiotomy nor tear. Among women who experienced perineal trauma, amoxicillin and clavulanic acid was protective against infection in all subgroups compared to placebo with no significant interaction between subgroup and trial allocation (p=0.17).2925 women were included in the multivariable risk factor analysis. Episiotomy was associated with an adjusted risk ratio of infection of 2.94 (95% confidence interval 1.62-5.31), forceps 1.37 (95% confidence interval 1.12-1.69) compared to vacuum extraction, primiparity 1.34 (95% confidence interval 1.05-1.70), amoxicillin and clavulanic acid administration 0.60 (95% confidence interval 0.51-0.72), body mass index 25-29.9 kg/m2 1.21 (95% confidence interval 1.00-1.47) and body mass index ≥30 kg/m2 1.22 (95% confidence interval 0.98-1.52) compared to body mass index <25 kg/m2. Each 15-minute increment between birth and antibiotic administration was associated with a 3% higher risk of infection (adjusted risk ratio 1.03, 95% confidence interval 1.01-1.06). results CONCLUSION: Timely prophylactic antibiotics should be given to all women after operative vaginal birth, irrespective of type of perineal trauma. The use of episiotomy, forceps, primiparity and overweight are associated with an increased risk of confirmed or suspected infection following operative vaginal birth. CONCLUSION: