Many more women should be offered long-lasting birth control such as the contraceptive jab, the body advising the NHS in England and Wales says.
It can be difficult to remember to take the pill each day
The National Institute for Health and Clinical Excellence estimates the move would cut the number of unplanned pregnancies by 70,000 each year.
In 2003-4, only 8% of women aged 16-49 used long-acting contraceptives, which also include implants and the coil.
That compared with 25% who took the Pill and 23% who relied on condoms.
The National Institute for Health and Clinical Excellence (NICE) says that the advantage of the long-lasting birth controls is that women do not have to remember to use contraceptives every day or each time they have sex.
It has now issued guidance for England and Wales saying that long-acting reversible contraceptive (LARC) methods should be offered to all women seeking advice on contraception.
But campaigners have warned that encouraging increased use of these methods could help fuel promiscuity and the rise of sexually transmitted infections.
Unplanned pregnancies per 1,000 women using:
Combined oral contraceptive pill - 80
Intrauterine device or system - 1 to 2
Injection - 1
Implants - less than 1
About 30% of pregnancies in Britain are unplanned, it is estimated.
Some of these are down to failure to use contraceptive as directed, such as remembering to take the Pill.
By contrast, LARC methods such as implants, injectible contraceptives, and coils - namely intrauterine devices and the intrauterine system- are less susceptible to incorrect usage.
NICE estimates that if 7.7% of women switched to long-acting contraceptives, there could be 70,000 fewer unplanned pregnancies in England each year.
Its new guidelines aim to promote greater contraceptive choice for women, which, in turn, could help reduce unplanned pregnancies and abortion rates.
Department of Health figures show there were 185,400 abortions in 2004 in England and Wales - a rise of 2.1% from 181,600 in 2003 and about 5.3% from 176,000 in 2002.
It would also be cheaper for the NHS if more women used LARC methods, NICE calculates.
Dr Chris Wilkinson, a consultant in sexual and reproductive health who helped develop the guidelines, said: "Expert clinical opinion is that LARC methods may have a wider role in contraception and their increased uptake could help to reduce unplanned pregnancy.
"The current limited use of LARC suggests that healthcare professionals need better guidance and training so that they can help women make an informed choice."
Professor Allan Templeton, President of the Royal College of Obstetricians and Gynaecologists said: "Women should be presented with all available choices of contraception, including long-acting reversible methods, as well as all known risks and benefits.
"This will ensure that women can choose and manage, after consultation with their doctor, their own contraceptive needs.
"Overall, LARC methods are not only more cost-effective than the combined oral pill but are also more effective at reducing unintended pregnancy.
But campaigners Norman Wells, director of Family and Youth Concern, said NHS money would be best spent highlighting the benefits of faithful and long-term relationships rather than indiscriminately promoting contraception.
"A far more effective way of achieving cost savings to the NHS would be to spell out the positive physical and emotional benefits of confining sexual intimacy to a faithful, lifelong relationship between a husband and wife."
Toni Belfield of the Family Planning Association said women should be given every opportunity to make an informed choice about what contraceptive method best suits them.
"We know from the 100,000 enquiries our helpline receives every year that women do not know enough about the range of contraceptive choices including long-term methods."
Jan Barlow, chief executive of Brook, welcomed the guidelines but stressed that LARC methods did not protect against sexually transmitted infections, and young people must also be encouraged to use condoms.
Matthew O'Gorman, spokesman for pro-life charity Life, told BBC Radio 4's Today programme: "To advise young people that they should be taking implants which will mean that there is less likelihood of them conceiving will just further encourage promiscuity and risky sexual behaviour.
"This will lead to a further increase in the sexually-transmitted infections that we are fighting against."
Baroness Gould, chair of the Independent Advisory Group on Sexual Health and HIV called on the government to monitor PCTs' provision of contraception.