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One in four pregnancies ends in an abortion each year, global estimates from the World Health Organization and Guttmacher Institute suggest.

The report in the Lancet said 56m induced abortions take place annually - higher than previously thought.

Researchers acknowledge rates have improved in many rich countries but warn this masks no change in poorer areas over the past 15 years.

Experts are calling for new approaches to contraceptive services.

New approaches

Scientists say the annual number of abortions worldwide increased from 50 million a year between 1990-1994 to 56 million a year between 2010-2014.

The rise in numbers is mostly seen in the developing world - driven in part by population growth and by a desire for smaller families.

Their calculations show that while the number of abortions per person has stayed stagnant in many poorer areas, in richer areas it fell from 25 to 14 per 1,000 women of reproductive age.

Researchers point out that abortion rates were similar across countries - regardless of whether terminations are legal or not.

They argue that laws banning abortions do not limit the number of terminations and can instead lead people to seek illegal abortions that can be unsafe.

The report goes on to highlight areas such as Latin America where one in three pregnancies ends in abortion - higher than any other region in the world.

And the study says there was a slight increase in abortion rates in Western Europe - which researchers suggest could be linked to an increase in women migrating from Eastern Europe and further afield.

'Stigmatised'

It is possible that some are not aware of the contraceptive services available or come from countries where abortion rates are higher in general, researchers say.

Dr Bela Ganatra, from the WHO, said: "The high rates of abortion seen in our study provide further evidence of the need to improve and expand access to effective contraceptive services.

"Investing in modern contraceptive methods would be far less costly to women and to society than having unwanted pregnancies and unsafe abortions."

But the study suggests the solution is not as simple as improving access to contraceptives.

Many women said they chose not to use contraceptives because they were worried about side effects, felt stigmatised or thought there was a low risk they would become pregnant.

Writing in a linked article, Dr Diana Greene Foster, of the University of California, San Francisco, said there was no one-size-fits-all technological answer.

She added: "That health concerns and dislike of contraceptive side-effects are so common across countries, indicates a need for development of new methods of contraception and a woman-centred approach to contraceptive provision."