Unsafe abortions in the developing world kill 68,000 women a year, research suggests.
Clean equipment is not always used
They also lead to at least five million other people going to hospital for infection and other complications, the Lancet study estimates.
A team from New York's Guttmacher Institute made their estimate after analysing data from 13 countries.
They suggested around 19 million unsafe abortions take place around the world each year.
That tally includes back-street pregnancy terminations as well as legal ones.
The researchers, funded by the pro-abortion Hewlett Foundation, said by comparison, in developed countries complications from abortion procedures or people going to hospital were rare.
Egypt, Nigeria, Uganda, Bangladesh, Pakistan, the Philippines, Brazil, Chile, Colombia, Dominican Republic, Guatemala, Mexico and Peru were examined. Some data for Burkina Faso, Ghana, Kenya and South Africa was also available.
The highest annual rate of hospital admissions was in Uganda, with 16.4 per 1,000 women. The lowest rate was in Bangladesh, with 2.8 per 1,000 women.
On average, the annual rate of hospital admissions was 5·7 per 1,000 women in all developing regions, excluding China.
Call for legalisation
Lead researcher Dr Susheela Singh said: "The evidence shows that the health burden of unsafe abortion is large.
"The most effective way of eliminating this highly preventable cause of maternal illness and death, would be to make safe and legal abortion services available and accessible.
"A second, more immediately achievable, goal is to prevent unintended pregnancies in the first place through improved contraception use."
Also writing in The Lancet, Marge Berer, editor of the journal Reproductive Health Matters, said the study painted a grim picture.
"The burden of injury and hospital admission are all the worse for being almost always avoidable.
"When legal restrictions on abortion are reduced, the rate of deaths and morbidity decreases greatly."
Any procedure to terminate an unintended pregnancy done by individuals lacking the necessary skills and/or in an environment that does not meet basic medical standards is deemed unsafe by the World Health Organization.
Paul Tully, general secretary of the Society for the Protection of Unborn Children, said Dr Singh's findings were guesses based on estimates.
"The burden of the study is clearly to promote the killing of more unborn babies in poorer countries, regardless of the fact that women do not want abortions," he said.
He also took issue with the notion liberalisation of abortion laws led to a cut in death and disability among pregnant women.
"This is contradicted by hard data from Poland, which imposed new legal restrictions on abortion in the mid 1990s and consequently showed improved maternal and infant health."