Allowing women to obtain a full year's supply of birth control pills, instead of one or three-month's worth at a time, could lower the number of unintended pregnancies and abortions, according to a California study.

The researchers estimate that if all the women in the study had received full one-year supplies of birth control pills, they would have had 1,300 fewer unintended pregnancies and 300 fewer abortions in 2006.

Most women are only able to get one or three-month supplies of birth control pills at a time. Some states, such as California, do have publicly funded programs that allow lower-income women to receive a full year's supply at once from a clinic (but not a pharmacy). But Medicaid patients are only allowed a one-month supply of any prescription drug by most states and rarely qualify for these programs.

Maybe they should.

The study looked at more than 84,000 lower-income women who received birth control pills through a California family program in January 2006. About 10% of these women received a full year's supply. The researchers then looked at birth records for the year 2006.

After adjusting for other factors that affect birth rate, such as age, ethnicity and previous contraceptive use, the researchers found that women who received the one-year supply were 30% less likely to have an unplanned pregnancy and 46% less likely to have an abortion in 2006 than those who received smaller supplies (the effect was even stronger before making these adjustments).

The findings don't prove that larger supplies of birth control pills lead to fewer unwanted pregnancies. But that's what they suggest. Women can't take birth control pills that they don't have.

The authors speculate that limits on birth control pills may be designed as a cost-cutting measure to prevent the waste of unused pills if a woman decides to stop taking them during the course of a year. But unintended pregnancies lead to even higher costs, both financial and emotional.

The researchers estimate that if all the women in the study had received full one-year supplies of birth control pills, they would have had 1,300 fewer unintended pregnancies and 300 fewer abortions in 2006. Bean counters should note that these were publicly funded pregnancies and abortions.

Nationwide, about three-quarters of all women taking birth control pills receive a three-month or smaller supply. Nearly half receive a one-month supply and need to return every month for more.

Dispensing more pills at a time might work better.

The study results appear in the March 2011 issue of Obstetrics & Gynecology.