Letting women have a year’s supply of birth control pills might help prevent more unwanted pregnancies, a new study suggests.

Right now, private and public health insurance plans in the U.S. generally limit how many months’ worth of birth control pills can be prescribed at once.

But researchers found that lower-income California women who got a year’s supply of the Pill had fewer unplanned pregnancies than women who got only enough packages for one or three months at a time.

For every 1000 women who participated in the study, 10 in the longer-supply group became pregnant within a year, compared to 30 of those who could only get prescriptions for shorter supplies.

The study also showed that when doctors prescribed a full year’s worth of pills, about two of every 1000 women had a state-funded abortion in the following year. But among women who had to come back every month or every three months for another prescription of the pills, roughly six of every 1000 had a state-funded abortion.

The findings, reported in the journal Obstetrics & Gynecology, do not prove that longer lasting Pill prescriptions will prevent unwanted pregnancies and abortions.

But that is what the results suggest, according to lead researcher Dr. Diana Greene Foster of the University of California, San Francisco.

“The implication of our finding is that health programs and insurance policies would likely save money and improve quality of care by dispensing a year’s supply,” Foster told Reuters Health in an email.

As it stands, in California and a few other states, publicly funded programs let lower-income women who do not otherwise qualify for Medicaid get a year’s worth of birth control pills from a family-planning clinic, like Planned Parenthood (but not a pharmacy).

Women who do qualify for Medicaid, however, fall under that program’s rules - and most state Medicaid programs routinely limit prescription drugs to a roughly one-month supply, Foster said.

Nationwide, she noted, about three-quarters of U.S. women on birth control pills receive no more than a three-month supply at a time.

Her study involved more than 84,000 lower-income women who received birth control pills through California’s family-planning program in January 2006. About one in 10 received a one-year supply.

The study was not perfect. For one thing, it only included women in California’s Medi-Cal program, rather than women from all walks of life. Also, the results would have been more reliable had participants been randomly (i.e., by chance) assigned to receive a longer or shorter supply of pills.

The researchers did try to account for factors that might have affected the results. For example, even when they considered the women’s age, race and history of birth control use, getting a one-year supply was still linked to a reduction in the odds of unplanned pregnancy and abortion over the next year.

Foster said a year’s supply of pills may allow more women to take them without interruption.