One quarter of all pregnancies ends in an abortion each year, new global estimates suggest.
Research from the World Health Organisation and Guttmacher Institute found that the annual number of abortions worldwide increased from 50 million per year between 1990-1994 to 56 million per year between 2010-2014.
While the researchers noted a decrease in the amount of abortions happening in developed countries, there was a significant increase in the amount of abortions occurring in poorer countries, resulting in a higher overall figure.
Experts have now called for an improvement in contraception available in developed countries to limit unwanted pregnancy.
According to the researchers, in developed countries abortion has declined as a proportion of all pregnancies from 39% in 1990-94 to 28% in 2010-14.
They said this was likely due to the fact that abortion rates have more than halved in Eastern Europe (88 per 1000 women to 42) as modern contraceptive methods have "become more widely available".
However, in developing countries abortion increased from 21% of pregnancies in 1990-94 to 24% in 2010-14.
In Latin America, a region with highly restrictive abortion laws, one in three pregnancies (32%) ended in abortion in 2010--2014, higher than any other region.
Dr Bela Ganatra, from the WHO, commented: "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."
The study found that abortion occurred at similar rates in countries where it is legal and where it is prohibited. For example, in countries where abortion is prohibited altogether, or allowed only to save a woman's life, the rate is 37 abortions per 1000 women, compared with 34 where it is legally permitted on request.
The overall abortion rate in Africa, where the vast majority of abortions are illegal, remained virtually unchanged at 33 abortions per 1000 women in 1990-94 and 34 per 1000 in 2014.
Gilda Sedgh from the Guttmacher Institute commented: "More women living in countries with the most restrictive abortion laws have an unmet need for contraception - that is, they want to avoid getting pregnant but are not using a method of family planning - than women in countries with more liberal laws, and this adds to the incidence of abortion in countries with restrictive laws."
The findings are published in full in the Lancet journal.
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