Kimberly Daniels, Jo Jones and Joyce Abma -- researchers at the National Center for Health Statistics, part of the Centers for Disease Control and Prevention -- found 59 percent of the women who had ever used emergency contraception had done so once, while 24 percent said they had used it twice.
The National Survey of Family Growth found about a quarter of young adult women ages 20-24 were most likely to have ever used emergency contraception, while 1-in-5 never-married women said they had used it, 1-in-7 cohabiting women said they used it and 1-in-20 currently or formerly married women said they had used emergency contraception.
About half of the women reported using emergency contraception because of fear of contraceptive failure and about half reported using it because they had unprotected sex, the researchers said.
The U.S. Food and Drug Administration first approved emergency contraceptive pills in 1998. Today there are at least four brands of emergency contraceptive pills, and most are available over-the-counter for women ages 17 and older, the report said.
Although insertion of a copper intrauterine device can be used for emergency contraception, the report focused only on emergency contraceptive pills.
The researchers noted not all women had access to emergency contraception during the earlier portion of their reproductive years.
Charlize Theron not engaged to Sean Penn 'yet'
Pregnant Mila Kunis wins 'Best Villain' at MTV Movie Awards