Around one-quarter of the world's women ages 20-24 were married as child brides, according to statistics gathered in the period from 2005-2012 and released recently by Unicef. The report was published ahead of celebrations for International Women's Day Tuesday, a holiday often used to honor women's roles in public life and lobby for equality.

Child marriage, defined as a marriage where one or both of the parties is under 18 (and frequently, under 15), can affect both genders, though girls are disproportionately affected. Child marriage was most prevalent in South Asia, according to the report, where nearly half of all women were married before age 18 and one in six were married before age 15. The rates of child marriage among boys hovered around 10 percent.

"Marriage before the age of 18 is a fundamental violation of human rights," read a summary from the report, adding: "Many factors interact to place a girl at risk of marriage, including poverty, the perception that marriage will provide ‘protection’, family honor, social norms, customary or religious laws that condone the practice, an inadequate legislative framework and the state of a country's civil registration system."

While controversy surrounding child brides does not frequently make headline news, the phenomenon is widespread and ongoing. A highly publicized incident in 2012 in Afghanistan highlighted the problem of violence and rape involved in child marriages.

Sahar Gul was married at age 13 after her father died and her brother’s wife no longer wanted to take care of her, the New York Times previously reported. Ghulam Sakh, around age 30, gave Gul’s brother $5,000 for the girl’s hand in marriage, despite the fact she was younger than the legal age for marriage, which is 15 at the earliest in Afghanistan.

When the girl refused to prostitute herself or have sex with Sakh, her inlaws locked her in a windowless cellar and beat her for months. The case was widely covered in Afghan and international media; and while Gul’s case was treated as extreme, violence against child brides is prevalent throughout the world.