Factors associated with infection after operative vaginal birth—a secondary analysis of a randomized controlled trial of prophylactic antibiotics for the prevention of infection following operative vaginal birth

Abstract

A recent randomized controlled trial of prophylactic antibiotics for the prevention of infection following operative vaginal birth showed that women allocated prophylactic intravenous amoxicillin and clavulanic acid had a significantly lower risk of developing confirmed or suspected infection within 6 weeks after operative vaginal birth (risk ratio [RR], 0.58; 95% confidence interval [CI], 0.49-0.69; P < .001). Some international and national guidelines have subsequently been updated to include prophylactic antibiotics after operative vaginal birth. However, the generalizability of the trial results may be limited in settings where the episiotomy rate is lower (89% of women in the trial had an episiotomy). In addition, there was a high burden of infection in the prophylactic antibiotics group despite the administration of prophylactic antibiotics. It is essential to identify modifiable risk factors for infection after operative vaginal birth, including the timing of antibiotic administration. 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 the timing of antibiotic administration. This study was a secondary analysis of 3225 women with primary outcome data from the prophylactic antibiotics for the prevention of infection following operative vaginal birth 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. Of the 3225 women 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 administration was protective against infection in all subgroups compared with placebo with no significant interaction between subgroup and trial allocation (P=.17). Moreover, 2925 women were included in the multivariable risk factor analysis. The following were associated with adjusted risk ratios of infection: episiotomy, 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 of 25.0 to 29.9 kg/m2, 1.21 (95% confidence interval, 1.00-1.47), and body mass index of ≥30 kg/m2, 1.22 (95% confidence interval, 0.98-1.52) compared to body mass index of <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). Timely prophylactic antibiotics should be administered to all women after operative vaginal birth, irrespective of the type of perineal trauma. The use of episiotomy, forceps birth, primiparity, and overweight were associated with an increased risk of confirmed or suspected infection after operative vaginal birth.