Thousands of women every year could be spared painful and occasionally life-threatening infections if doctors administered preventive antibiotics after every assisted childbirth, a major trial has found.

A single dose of antibiotics within six hours of childbirth nearly halved the number of infections in women whose babies were delivered with either forceps or ventouse suction cups, procedures that are used in one in eight UK births.

The trial involving 3,420 women who gave birth in 27 units across Britain suggests that this could prevent 7,000 maternal infections in the UK, and more than 200,000 maternal infections worldwide annually.

The findings, described as “practice-changing” by doctors not involved in the trial, will be reflected in new advice to be published by the UK’s Royal College of Obstetricians and Gynaecologists this year.

“This will have a very big impact on women and not just in terms of the infection rate,” said Marian Knight, a professor of maternal and child population health at the University of Oxford. “Those who received antibiotics were much less likely to have perineal pain, much less likely to have burst stitches, and they had fewer problems feeding their baby as a consequence of that pain.”

Forceps and ventouse suction cups can raise the risk of infection by introducing microbes into the genital tract. But women who have assisted childbirth also tend to be in labour longer, have more vaginal examinations, are fitted with urinary catheters more often, and have more tears and surgical cuts than those who give birth spontaneously.

All can increase the risk of infection, which in rare cases can develop into life-threatening sepsis. In developed countries, infections account for about one in 20 maternal deaths. For every fatal infection, a further 70 women develop infections that are serious enough to cause long-term health problems.

Between March 2016 and June 2018, women who took part in the trial were randomly assigned to have either an antibiotic (amoxicillin and clavulanic acid), or a saline placebo, administered intravenously within six hours of childbirth. Overall, a third of the births were ventouse and two-thirds of the babies were delivered by forceps.

In the placebo group, 19% of women picked up an infection soon after childbirth, compared with 11% in the antibiotic group. More serious cases of sepsis, confirmed by a positive blood test, reached 1.5% in the placebo group, but only 0.6% in the antibiotic group, according to a report in the Lancet.

“I was surprised by the proportion of women who got an infection,” said Knight. “The majority are not serious, life-threatening infections, but they do need to be caught early to make sure they don’t progress to those major infections.”

By protecting women against infections immediately after giving birth, overall antibiotic use fell, the doctors found. For every 100 doses of antibiotics given prophylactically, clinicians avoided the need to give 168 doses for infections that took hold after childbirth.

The lower rate of infections among the women given antibiotics had a knock-on effect on their broader recovery from childbirth, according to the trial. Compared with the placebo group, women who had antibiotics were less likely to be treated for burst stitches and perineal pain, and reported fewer outpatient appointments due to their wounds, or home visits from GPs, nurses or midwives.

The researchers estimate that, on average, the cost to the NHS six weeks after birth was £102.50 for each woman who had the antibiotics, compared with £155.10 for the placebo group.

In an accompanying editorial, Vincenzo Berghella of Thomas Jefferson University in Philadelphia described the findings as “practice-changing” and called for clinical guidelines for obstetricians to be updated.

Pat O’Brien, a consultant obstetrician and spokesperson for the Royal College of Obstetricians and Gynaecologists, said: “This is a very interesting and well-conducted trial. Around 12% of women in the UK have an assisted birth and these results show that single dose antibiotic use could reduce infections by half – equivalent to around 7,000 infections every year.

“It is standard practice to provide single-dose antibiotic to all women who have a caesarean birth to reduce infection, and it follows that this should be considered for women following an assisted birth.

“Based on these findings alone, it does seem that routine use of a single dose of antibiotic following an assisted birth would help to reduce infections and ensure the best possible health outcomes for women, as well as reduce costs of complications for the health service.”