“Or,” she said, “it could be that being given a year’s supply may enhance the expectation that the method is acceptable and safe, while fewer packs may encourage the woman to reconsider use of the method at each re-supply visit.”

Foster thinks health plans’ limits on birth control pills are probably meant to control costs. If a woman decides to stop using them over the course of a year, then some pills will go to waste.

But Foster and her colleagues estimate that giving a year’s supply to all the women in their study would have prevented almost 1,300 pregnancies and 300 abortions paid for by the state.

A month’s supply of birth control pills costs anywhere from $15 to $50, according to Planned Parenthood.

SOURCE: Obstetrics & Gynecology, March 2011.