Melinda Gates has pledged more than half a billion dollars ($560 million US) as part of a global campaign to extend contraception advice and services to millions of women in the world's poorest countries.

The funding pledge came Wednesday at the London Summit on Family Planning, which was co-hosted by the British government and the Bill and Melinda Gates Foundation — the foundation that was established by the Microsoft founder and his wife to fight poverty and improve global health.

Governments and charitable foundations at the summit committed to spend $4.4 billion over the next eight years to help 120 million of the estimated 220 million women who currently have no access to contraception or family planning services.

The summit's organizers say a commitment of that size could be enough to prevent 200,000 maternal deaths during pregnancy and childbirth by 2020.

They also say it could mean almost three million fewer infants dying in their first year of life.

"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."

As many as 80 million unintended pregnancies will occur in the world's developing countries this year.