WASHINGTON — Women who need a C-section should get antibiotics before, not after, they're cut -- preferably within an hour of the start of surgery, says a new guideline for obstetricians in the United States.

Infection occurs in 10 per cent to 40 per cent of women who undergo a caesarean delivery, making it the most common complication, according to the American College of Obstetricians and Gynecologists. In comparison, three per cent or fewer women who deliver vaginally get an infection.

Antibiotics have long been given for C-sections to reduce that risk, but usually not until right after the baby was born. That was a precaution in case the antibiotics made it into the baby's bloodstream and prevented newborn testing from spotting an already brewing infection; another concern was the potential to spur antibiotic-resistant germs.

ACOG's new guideline, released Monday, cited recent studies that concluded an intravenous infusion of antibiotics before surgery reduces the chance of a mother's infection without harming the newborn. The guideline, published in the journal Obstetrics & Gynecology, said women who need an emergency C-section should get the antibiotics as soon as possible, while those already taking antibiotics for another reason are exempt.