Objective To perform a cost utility analysis of prophylactic antibiotics compared with a placebo in preventing maternal infection after operative vaginal birth. Design Economic analysis based on the findings of the ANODE trial, a multi-centre randomised placebo‐controlled trial. Setting Twenty-seven hospital obstetric units across the UK. Population or Sample Women who underwent operative vaginal delivery after at least 36 weeks of gestation. Methods A cost utility analysis from the perspective of the National Health Service was performed. To inform the decision analysis, a decision tree was constructed to calculate an incremental cost effectiveness ratio (ICER). Two one-way sensitivity analyses were conducted. Main Outcome Measures Difference in quality of life and cost between patients given the antibiotics and the placebo. Quality of life scores were reported EQ-5D-5L measurements from the ANODE trial. Results The ANODE trial reported a statistically significant reduction in infection rates with the co-amoxiclav intervention, this was found to yield an improvement of 0.017 QALYs over the placebo1. The cost to the NHS of the intervention was also lower at £120 over 6 weeks compared to the placebo’s £194. This gives an ICER of -£4403.14/QALY. Sensitivity analysis confirmed that the intervention was dominant. Conclusions A prophylactic dose of co-amoxiclav following operative vaginal delivery is a cost-effective intervention, offering improved QoL whilst also reducing overall costs over a 6-week time period. Tweetable abstract Prophylactic antibiotics are a cost-effective way to reduce maternal infection after operative vaginal delivery.