A single injection of antibiotics significantly reduces the risk of infections when women who are giving birth require the aid of forceps or vacuum extraction, a new study concludes. The routine use of the prophylactic shot actually reduces antibiotic use in the long run, the study found.

British researchers randomly assigned 3,420 women who had operative vaginal births to one of two groups: The first received a single shot of Augmentin (amoxicillin and clavulanic acid) within six hours of giving birth, and the second a placebo saline shot. Then they tracked infections over the next six weeks. The study is in Lancet.

Compared with the placebo group, women who got the antibiotic had a 42% reduced risk for any infection, and a 56% lower risk of a body-wide infection. Antibiotic users had about half the risk of perineal wound infection compared with the placebo group, and they used less pain medication. The researchers calculated that for each additional 100 doses of antibiotic used preventively, 168 doses of antibiotics to treat infections would be saved.

“The evidence is very clear,” said the lead author, Dr. Marian Knight, a professor at the University of Oxford. “There is a benefit in a single dose of antibiotics after operational birth — less chance of infection, less chance of pain, less chance of problems with the wound. And we’re actually reducing the amount of antibiotics that would be used.”