Women over 35 are increasingly having abortions as they are under the illusion they are "too old" to conceive, leading them to shun contraception.
The British Pregnancy Advisory Service, Britain's largest abortion provider under the NHS, has warned that over four in 10 women in their late 30s and 40s are not using contraception.
Many women believe they do not need to use contraception as they can only become pregnant through IVF, when the chances of conception are still relatively high. Warnings that career women are leaving it too late to have a child are partly to blame, Bpas added.
Ann Furedi, chief executive of Bpas, told the Telegraph: "Over the past few years we have seen much scaremongering about older women's fertility. From 'career women' leaving it too late to older women 'banking on IVF' to conceive, these stories lead many women to dramatically underestimate their own fertility later in life."
Figures from the Department of Health show that abortion rates among women in this age group have been on the rise, but have fallen among others.
Since 2001, the rate has risen by 15.5% for women aged between 30 and 34 and by 6% for women over 35.
In 2002, the number of abortions stood at 6,531 for women aged between 40 and 44, which rose to 7,737 in 2012.
Additional research by Bpas showed that of the 156,751 women having abortions between 2011 and 2013, women in their late 30s and 40s were far less likely to use contraception than younger age groups. Over 42% of women in their 40s had not used protection of any form, compared to 34% in their late 20s.
Experts said that messages to avoid delaying motherhood have gone too far and may now be encouraging women to assume it is safe to avoid contraception entirely.
"At Bpas we see more women over 35 with unplanned pregnancy than we do women under 18," Furedi added. "We know from speaking to women that stories and campaigns suggesting it's hard to get pregnant after 35 – even if well intentioned – are having a real impact on women's perception of their own fertility, and therefore their use of contraception.
"Women deserve accurate, impartial information to make their own choices about family planning in their 30s. Fertility does decline as you get older, but the drop is not as great as we are sometimes led to believe."
She advised: "For women who don't want to fall pregnant the message is simple: use contraception until you have passed your menopause."
The number of women delaying motherhood to conceive later in life has risen. Earlier this year, Professor Dame Sally Davies, chief medical officer for England, also highlighted that more women were choosing not to have children at all, as 20% reach middle age without offspring.