Melinda Gates has pledged $560 million as part of a campaign to expand access to contraception for women in some of the poorest countries in the world.
Supporters of the campaign estimate that this year will see 80 million unintended pregnancies in developing countries. They say 800 women die every day as a result of pregnancy-related complications - the leading cause of death for teenage girls in the developing world.
"When I travel and talk to women around the world they tell me that access to contraceptives can often be the difference between life and death," Gates said.
"Today is about listening to their voices, about meeting their aspirations, and giving them the power to create a better life for themselves and their families."
Government officials and aid agencies said the involvement of the Bill and Melinda Gates Foundation, set up by the Microsoft founder and his wife, would help re-frame a debate that has been controversial since the forced sterilizations in India in the 1970s and China's one-child policy.
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