Yet only about five to six percent of U.S. women who use contraception choose those methods.

Based on the current findings, Eisenberg said, many more women might choose them if they had full information and full coverage of the cost.

The study included 4,144 St. Louis-area women who were surveyed before getting contraceptive counseling. They were asked to rate the effectiveness of different birth control options, picking from a list of choices.

Overall, 45 percent overestimated the Pill, condoms, the hormonal patch, the hormonal vaginal ring and the injection hormone Depo-Provera. (It was not possible to overestimate the effectiveness of IUDs or implants because of the survey’s structure.)

Then, after the women were counseled on all their options, a full 71 percent chose an IUD or implant.

That suggests that when you “remove the obstacles,” Eisenberg said, many women want those contraceptives.

Besides lack of awareness, those obstacles include cost.

IUDs and implants have a big “upfront” cost: the Mirena IUD itself has gone up over the years and is now nearly $800. The ParaGard price tag is about $500. Then there are the doctor’s charges.

The Implanon implant costs between $400 and $800, with all charges considered.

Since the devices last for years, that cost may be worthwhile over time, Eisenberg pointed out. Birth control pills, for instance, cost anywhere from about $10 to $50 a month, depending on whether a woman uses generic or brand-name pills.

But if women don’t have full insurance coverage of the upfront cost, they may balk at the price tag.

The devices can have unwanted side effects, too. With the implant, irregular menstrual bleeding is most common; some women stop having their periods altogether.

The Mirena IUD may also cause menstrual irregularities. But it generally makes periods lighter, which is why it is also approved as a treatment for heavy bleeding. The ParaGard IUD has the opposite effect: menstrual bleeding and cramping can increase, though that may go away over time.

Eisenberg, who has already presented some of the current findings at a medical conference, said he thinks IUDs and implants should be the “default” options offered to women seeking reversible birth control.

But that’s not what many doctors are doing, he noted.

If women can’t get the contraceptives from their own doctor, Eisenberg said, they may be able to find a family planning center that can provide them.

SOURCE: American Journal of Obstetrics and Gynecology, online April 9, 2012.