I spent most of my time this year advocating for better access to family planning around the world. Early on, I told everybody who would listen that I wanted to help put contraceptives back on top of the global health and development agenda. Visiting women in developing countries, however, I realized that this framing didn't quite capture my message.

Contraceptives are tools, and the development agenda is an abstract construct. What was missing were human beings, the women across the world who have told me over and over again that having access to birth-control methods that work for them would change their futures. Now I tell people that I want to help put women at the center of global health and development work, and better contraceptives are one of their top priorities. Listening to women shouldn't still be a revolutionary idea in 2012, but it is.

When I visit family-planning wards at health clinics in African countries, there are always plenty of free condoms available. Condoms are vitally important, especially because they also help prevent the spread of sexually transmitted diseases like AIDS. But there's a problem: The overwhelming majority of African women can't rely on condoms for birth control because their husbands refuse to use them.

In the same way that American women prefer contraceptive pills, which they don't have to negotiate with their partners, African women favor contraceptive injections over condoms. But because of supply constraints, supply-chain problems and outdated public policies, these injections are frequently out of stock. To take one example, in Kaduna, Nigeria, a city of some 1.5 million people, there were 226 days last year when not a single public health clinic had injections available.

If you are focused simply on making sure contraceptives are available, you can stockpile condoms and call it a day. But if your goal is helping women build the lives they want for themselves and their families, the bar is higher.

In the United States, especially this year, any occasion when contraceptives and public policy overlap seems to be an excuse to fight about other issues — abortion or the meaning of religious freedom, for instance. But the fact is, literally 99 percent of women in the United States who have had sex use birth control at some point in their lives. What our behavior (if not our rhetoric) tells me is that contraceptives matter to us. They certainly mattered to me. I was able to go to college and business school. I was able to have a rewarding career at Microsoft. And then Bill and I were able to decide how many children to have (three) and when to have them (each three years apart), which I believe made us better parents.

These are some of the same reasons that contraceptives matter to women in developing countries. Like all parents, they want their children to grow up healthy and go to school. Contraceptives don't do all this, of course. They are a single link in a long chain that includes proper nutrition, vaccines, clean water, productive farms and high-quality public schools. But they are the first link, and they give parents a much better opportunity to complete the chain. As one young mother in Kenya told me, "I want to bring every good thing to my child before I have another."

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There are convincing data showing the long-term impact of contraceptives. The leading study, ongoing in Bangladesh for the past 35 years, proves that people who have access to and education about contraceptives have a higher quality of life in almost every conceivable way than those who don't. They are healthier, less likely to die in childbirth, and less likely to have children who die. They are better educated, with sons and daughters who have more schooling. And they are more prosperous: Their households have more total assets, including land, livestock, and savings. On an even larger scale, economists have argued convincingly that the so-called East Asian economic miracle of the 1980s was due in large part to parents in the region deciding to have fewer children.

Contraceptives unlock one of the most dormant but potentially powerful assets in development: women as decision-makers. When women have the power to make choices about their families, they tend to decide precisely what demographers, economists and development experts recommend. They invest in the long-term human capital of their families. They don't do it because they're worried about GDP; they do it because they're worried about their children's futures. But the two fit together beautifully.

Today I tell people that I want to help put women at the center of global health and development work — and that contraceptives are one of the best ways to do that. Because when women everywhere have the power to achieve their goals, they will be doing the majority of the work of development by themselves.

Gates, a 2012 Foreign Policy Global Thinker, is co-chair of the Bill & Melinda Gates Foundation.