WASHINGTON (AP) -- A major birth control study of nearly 10,000 women is under way in St. Louis that provides a clue about what might happen when a policy takes effect that will make contraceptives available free of charge as preventive care.

The study, called the Contraceptive CHOICE Project, provides free of charge various methods of birth control, from pills to intrauterine devices.

Jeffrey Peipert of Washington University in St. Louis says about 75 percent of women in the study are choosing the IUD or the implant because they're longer-lasting options that have a lower failure rate.

In the U.S., only about 5 percent of U.S. women choose that method.

It's expensive and can cost $600 to nearly $1,000 upfront to be inserted by a doctor without help from insurance.