Clarisse told a story that broke my heart:

I was 14... My mom and her sisters began to prepare food and my dad asked my brothers, sisters and me to wear our best clothes because we were about to have a party. Because I didn't know what was going on, I celebrated like everyone else. It was that day I learned that it was my wedding and that I had to join my husband. I tried to escape but was caught. So I found myself with a husband three times older than me... This marriage was supposed to save me from debauchery. School was over, just like that. Ten months later, I found myself with a baby in my arms. One day I decided to run away to stay, but I agreed to come back to my husband if he would let me go back to school. I returned to school, have three children and am in seventh grade.

Clarisse is now 17 years old, and her story of a lost childhood is, unfortunately, all too common, not just in her native Chad, but in many parts of the world. As the United Nations Population Fund's (UNFPA's) The State of World Population 2013: Motherhood in Childhood report succinctly puts it, "When a girl becomes pregnant, her present and future change radically, and rarely for the better." This is true everywhere, but the problem is most acute in the developing world, where 88 percent of all adolescents live. Every day, 20,000 girls below the age of 18 give birth in these developing nations.

Clarisse's story illustrates the sadness that attends so many childhood pregnancies, and the price young girls pay in missed opportunities for personal development. But many girls pay an even higher price. UNFPA's latest research confirms that pregnancy and childbirth are now a leading cause of death for females ages 15 - 19 in developing countries, with some 70,000 adolescent girls dying each year from causes related to pregnancy and childbirth. These statistics are particularly tragic because so many of these deaths are preventable.

In a world confronting so many problems, from natural disasters to armed conflicts to climate change, there is a natural inclination to say, "This is how it has always been, and probably how it will always be. Teen pregnancy is a terrible problem, but we have other priorities we need to address." And that would be a mistake. Because adolescent pregnancy isn't just a problem in Chad and for the nations of the developing world. It's a problem for us all.

More than seven billion of us now share a fragile ecosystem that provides inadequate food, water, shelter and sanitation to a sizable and growing percentage of the human population. And in many cases, population is growing fastest in nations with the fewest resources. Teen pregnancies are contributing to that population growth and damaging the economic potential of many nations in the developing world. If Kenya's more than 220,000 adolescent mothers had gotten jobs instead of getting pregnant, for example, it would have added $3.4 billion to the Kenyan economy, an amount equal to the nation's entire construction sector. And because the development of nations at the bottom of the economic ladder is vital to growth of the overall global economy, issues that handicap that growth hurt us all.

Adolescent pregnancy may pose special challenges to the nations of the developing world, but it is problem for developed nations as well. There are currently approximately 680,000 births to adolescent mothers in developed countries annually, with nearly half of those occurring in the United States. The additional costs to U.S. taxpayers for increased health care and foster care, as well as the costs generated by the increased incarceration rate of children of adolescent mothers, is estimated to total nearly $11 billion per year.

Adolescent pregnancy diminishes the life opportunities of girls everywhere, but the cost goes beyond the burden borne by the girls themselves. And that is why it is our collective responsibility to address this problem. We can start by thinking about adolescent pregnancy in new ways, beginning with the understanding that society -- not just the teenage girl -- is the source of the problem. We can advance the human rights of adolescent girls by adopting more enlightened attitudes about gender roles and gender equality. And we can follow that up with specific actions that have demonstrated their effectiveness in reducing adolescent pregnancy.

We must, for example, overcome harmful cultural traditions and historic prejudices, and end child marriage. And since we know that education is a strong prophylactic against teen pregnancy, we must find ways to keep girls in school. We also need to dramatically increase adolescents' access to age-appropriate sexual and reproductive health information and to contraceptive products. And we need to provide better support for adolescent mothers.

Clarisse's story is not over. As a young mother, she has found time to go back to school. She is years behind, but she is working hard to catch up. She, and young mothers like her around the world, need and deserve our help. But we can, and must, do more to help ensure that young girls never have to face the life choices Clarisse had to face. It is within our power to significantly reduce the incidence of adolescent pregnancy, and it is in our collective best interest to do it.

This opinion piece originally appeared in The Huffington Post

Follow Dr. Babatunde Osotimehin on Twitter: @babatundeunfpa