INTRAUTERINE devices (IUDs) should be used routinely in place of the "morning after Pill", experts said today.
The advice came after research showed "the coil" to be a far more effective form of emergency contraception.
IUDs consist of a small plastic and copper device inserted into the womb by a trained doctor or nurse.
They have been employed as a method of emergency contraception for at least 35 years. Used in this way, the device should be inserted within about five days of unprotected sex.
Researchers analysed data from 42 studies on emergency use of IUDs conducted in six countries between 1979 and 2011. The studies included eight different types of IUD and involved more than 7,000 women.
Overall the IUDs had a failure rate of just 0.09pc, compared with between 1pc and 3pc for two types of "morning after Pill".
The results were published today in the journal Human Reproduction.
Lead author Kelly Cleland, from Princeton University in the US, said: "Unintended pregnancies are a significant health problem worldwide. It is estimated that globally at least 36pc of pregnancies are unintended. We already know from previous research that IUDs are very cost-effective forms of regular contraception.
"This study is the most comprehensive review to date of the efficacy of IUDs used for emergency contraception, and our results provide clear evidence that they are a highly effective method of emergency contraception, as nearly 100pc of users overall did not become pregnant after unprotected sex when an IUD was inserted post-coitally.
"In contrast, failure rates are at least 10-20 times as high for emergency contraceptive pills such as ulipristal acetate and levonorgestrel.
"IUDs also offer very effective ongoing contraception. Therefore, we conclude that IUDs should be included routinely as an emergency contraceptive option whenever feasible and appropriate."
IUDs are most popular in China, where 43pc of women choose this method of contraception compared with 13pc in the rest of the world.