Lead author Dr. Jeff Peipert of Washington University School of Medicine in St. Louis said a Brookings Institution report this year found more than 90 percent of U.S. abortions occur due to an unintended pregnancy and each year 50 percent of all U.S. pregnancies aren't planned -- far higher than in other developed countries.
The Contraceptive Choice Project enrolled 9,256 women and adolescents in the St. Louis area from 2007 to 2011 -- ages 14-45 at risk for unintended pregnancy, and willing to start a new contraceptive method.
The women were counseled about different methods of contraception, their effectiveness and risks and benefits. The women were told of the failure rate of fewer than 1 percent of pregnancies for women using IUDs and implants. Shorter-acting forms of birth control such as oral contraceptives have a failure rate of 8 percent to 10 percent.
About 75 percent of women in the study chose IUDs or implants, Peipert said.
The study, published online in Obstetrics & Gynecology, said from 2008 to 2010, annual abortion rates among study participants ranged from 4.4 to 7.5 per 1,000 women -- a drop ranging from 62 percent to 78 percent compared to the national rate of 19.6 abortions per 1,000 women in 2008, the latest year for which figures are available.
Among girls ages 15-19 who had access to free birth control provided in the study, the annual birth rate was 6.3 per 1,000, far below the U.S. rate of 34.3 per 1,000 for girls the same age, the study said.
Cost was a major factor in the women choosing a contraceptive. IUDs and implants are inserted by healthcare providers and IUDs are effective for five to 10 years and implants for three years. However, few women use them because they cost about $800 and are often not covered by insurance -- if the women are insured, Peipert said.