Post-partum sepsis is thought to cause 11% of maternal deaths globally and in 2016, it is estimated that 19 500 women died because of pregnancy-related infections. Antibiotic prophylaxis at caesarean section is widely recommended because it reduces incidence of maternal infection, but current WHO guidelines do not recommend routine antibiotic prophylaxis for women undergoing operative vaginal birth because of insufficient evidence of effectiveness. In a blinded, randomised controlled trial done recently published in the Lancet, women aged ≥16 years were allocated to receive a single dose of intravenous amoxicillin and clavulanic acid or placebo (saline) after operative vaginal birth occurring at 36 weeks gestation or later. 1719 women received antibiotics, and 1708 placebo. Seven women withdrew, leaving 1715 in the amoxicillin and clavulanic acid group and 1705 in the placebo groups. Primary outcome data were missing for 195 (6%) women. Significantly fewer women who got the dose of antibiotics had a confirmed or suspected infection (180 [11%] of 1619) compared to women allocated to placebo (306 [19%] of 1606; risk ratio 0·58, 95% CI 0·49–0·69; p<0·0001). The authors conclude that guidelines could be revised to reflect the clinical utility of the approach.