The practice of child marriage, which is still widely prevalent in some parts of South Asia, the Middle East, and sub-Saharan Africa, is one of the principal reasons that fertility rates remain high in those areas. About 25,000 girls a day become child brides. As part of its coverage this year on world population at 7 billion, National Geographic features stories on the practice of child marriage in India and Yemen.
http://ngm.nationalgeographic.com/2011/06/child-brides/gorney-text