Melinda Gates has made providing poor women in developing countries access to contraception a mission. The Bill & Melinda Gates Foundation, which she leads with her husband, has donated more than $1 billion for family planning efforts and will spend about $180 million more this year.

Since 2012, she has helped lead an international campaign to get birth control to 120 million more women by 2020. Four years later, a report explains why achieving that goal is proving tougher than expected. This is a condensed and edited version of our conversation about family planning.

Why is this the cause of your life?

If you allow a woman — if you counsel her so it’s truly voluntary — to have a contraceptive tool and she can space those births, it unlocks the cycle of poverty for her. In the early days, I’d be out traveling for the foundation, I’d be there to talk to women about vaccines, I’m going be frank, for their children, and what they would say to me is: ‘O.K., I have questions for you. What about that contraceptive, how come I can’t get it anymore?’ To me, it’s one of the greatest injustices.

One of the statistics in the report that most struck me was that contraception prevented tens of millions of unsafe abortions by preventing unwanted pregnancies. You’re Roman Catholic. Is that part of the moral imperative for you?

Yeah. I mean this is obviously something I’ve had to wrestle with very deeply. The Catholic Church doesn’t even believe in these forms of modern contraceptives. I’m in the developing world minimum three times a year now, and I’m out in slums, in townships, in the rural area, and when you see a needless death of a woman or a child because she literally just didn’t have a very inexpensive tool that we not only believe in, we use in the United States — more than 93 percent of married Catholic women report using contraceptives — the moral imperative is that we give these women what we believe in and actually use.