Researchers have urged that girls as young as 11 and 12 years old should be fitted with coils after unprotected sex instead of being given the morning after pill.
They have calculated that it is almost 100 per cent effective at preventing pregnancies compared to the emergency pill which has failure rates of up to 3 percent.
Academics also say that the coils can prevent pregnancy for up to five days after sex, the Daily Mail reported.
An intrauterine device is a small, T-shaped contraceptive device made from plastic and copper that fits inside the womb.
It's a long-lasting and reversible method of contraception but can't stop you getting a sexually transmitted infections.
An IUD stops sperm from reaching the egg. It does this by releasing copper, which changes the make-up of the fluids in the womb and fallopian tubes. These changes prevent sperm from fertilising eggs.
IUDs may also stop fertilised eggs from travelling along the fallopian tubes and implanting in the womb.
It takes about 20 minutes for a doctor or nurse to insert an IUD in the womb.
They can be used as an emergency form of contraception up to five days after unprotected sex.
The morning after pill only works for 72 hours after sex - three days - and the failure rate increases the longer after sex a woman waits.
Professor James Trussell, from Princeton University in the US, said doctors and nurses should hand out coils to girls as young as 11 and 12.
The coils, known as intrauterine devices (IUD), are similar in size to matches and are fitted inside the womb for a maximum of five years.
They work by releasing copper which changes the fluids in the womb and prevents sperm reaching the egg.
The devices can be fitted only by certain doctors and nurses at surgeries or family planning clinics and the procedure lasts around five to ten minutes.
They cost at least 120 pounds to fit compared to about Ģ6 for a morning after pill.ut the researchers say that in the long-term they would work out to be far cheaper as they would prevent so many more pregnancies.
"There are a lot of people who would like to think the morning after pill is a panacea for red- ucing unwanted pregnancies because it's cheap," Professor Trussell, who specialises in Economics and Public Affairs at Princeton University, said.
"But unfortunately this is not the case. It protects against sex last night but it won't work three weeks from now.
"People who have unprotected sex regularly don't use it. Eventually they are going to get pregnant," the Professor said.
Women who took emergency contraceptive pills after unprotected sex were up to 20 times more likely to fall pregnant compared to those who had an IUD inserted
The findings are published in the journal Human Reproduction.