Experts have cautioned women over 35 not to abandon contraception in the mistaken belief that they cannot get pregnant past a certain age.
The Family Planning Association (FPA) believes the message on infertility and age has gone "too far".
Although fertility does wane as women get older, they can still fall pregnant well into their thirties, forties and even fifties.
Abortion rates for women aged 40 to 44 match those for the under 16s, figures for England and Wales show.
In 2008, both of these groups had an abortion rate of four per 1,000 women.
Julie Bentley, chief executive of the charity, said women should keep using contraception until after the menopause if they want to avoid pregnancy.
Young pregnant woman and with son in living room
The FPA said that the message about infertility is being "overplayed."
"Whilst the message about fertility declining with age is an important one, it is often overplayed, alongside disproportionate messaging about unplanned teenage pregnancies," Sky News quoted her as saying.
"It sends an inaccurate message to women and society that only the young become pregnant and is leading older women to believe their fertility has gone long before it actually has.
"It's important that women realise it's entirely conceivable that just one night of unprotected sex in your late 30s, 40s, even 50s can end in an unplanned pregnancy.
"Our helpline receives calls from such women, shocked this has happened to them. They thought their age would protect them from becoming pregnant," she added.