Women given a 12-month supply of oral contraceptives are less likely to have an unintended pregnancy than if they need to get refills every three months, US research suggests.

The authors used a computer model to look at the impact of reducing the number of times a woman would have to refill her contraceptive prescriptions on the risk of unplanned pregnancies and cost, using data from more than 24,000 women who had served in the military.