Dr. David L. Eisenberg of the St. Louis School of Medicine and Gina M. Secura, Dr. Tessa E. Madden, Jenifer E. Allsworth, Qiuhong Zhao and Jeffrey F. Peipert performed a cross-sectional analysis of a contraceptive knowledge questionnaire that had been completed by 4,144 women. The women were part of the Contraceptive CHOICE Project before they received comprehensive contraceptive counseling.
The study published in the American Journal of Obstetrics and Gynecology found 86 percent of study participants knew the annual risk of pregnancy was more than 10 percent if no contraception was used.
However, more than 45 percent of women overestimated the effectiveness of depo-medroxyprogesterone acetate (an injectable birth control drug), the pill, the patch, the ring and condoms.
After adjustment for age, education and contraceptive history, the data showed women who chose the intrauterine device or implant -- the most effective methods of birth control -- were significantly more likely to identify the effectiveness of their method accurately compared with women who chose either the pill, patch or ring, the study said.
Less than 1-in-100 women will get pregnant each year if they always take the pill each day as prescribed, but 9-in-100 women will get pregnant each year if they don't always take the pill each day as directed.
Male condoms are 82 percent to 98 percent effective at preventing pregnancy due to incorrect or inconsistent use, not the failure of the condom, the Centers for Disease Control and Prevention said.