Those risks are often substantial and the problem goes much deeper than you might think. Here, then, are several facts about child brides and what they face, compiled from a Human Rights Watch brief and other sources.
1. Child brides often die from pregnancy or childbirth
Child brides often become child mothers, frequently before their bodies are completely ready. In developing countries, where almost all child marriages take place, complications from pregnancy and childbirth are the No. 1 cause of death for girls age 15 to 19. That means that pregnancy and childbirth kill more girls in the developing world than war, AIDS, tuberculosis or any other cause.
The reason that pregnancy and childbirth kill so many girls is that their bodies are not ready. In developing countries, a girl or woman is twice as likely to die in childbirth if she's age 15 to 19 than she is if she's in her 20s. Girls under the age of 15 are five times as likely to die. Statistically, Nada al-Ahdal had real reason to fear that her marriage could kill her.
2. Child brides are typically far from equal partners in their marriage
This might seem like an obvious point, but its implications can be more pervasive than you might think. Keep in mind that husbands to child brides are typically adults and may have often paid her parents for the privilege; many activists consider child marriages to be a form of human trafficking, i.e. the buying and selling of human beings.
This dynamic can leave the child brides as the subject of their husbands, rather than their partners, which is why some activists argue that sex in such marriages should not be considered consensual.
3. The conditions of child marriage make marital rape more likely
UNICEF calls child marriage "the most prevalent form of sexual abuse and exploitation of girls."
Some activists argue that, in cases where the bride is clearly a young child, sex in such marriages should not be considered consensual. Separately, the fact that the husband may have paid for his bride can set up a dynamic that's more transactional than romantic. Comprehensive statistics on marital rape are not available and, in any case, what constitutes marital rape can be tough to define in places where a girl grows up learning that she's expected to do her "marital duty." Still, Human Rights Watch cites a number of anecdotal cases that clearly qualify as rapes, often justified as function of the girls' marriage.
4. Girls are often forced out of school when they marry
This is just one of the many knock-on effects of point number two. Girls who drop out of school in their early teens or even younger are often left totally reliant on their husbands. This leaves them with little future except as a housewife and mother, a life they never have the opportunity to choose willingly as an adult. Having dropped out of school so young also makes it that much tougher for them, because they have little means to provide for themselves, to leave their marriage if their husband is abusive.
5. Every year, 14 million girls become child brides, and that number is going up
That's 38,000 new child brides per day. Because child marriages are most common in countries where the population is growing, the overall number of child brides is expected to increase. In 2010, a study found that 67 million women age 20 to 24 had become married as children. The same study anticipated that this number would rise to 142 million by 2020.
6. Child marriages are more common in poorer, rural regions
This is true both between and within countries. In other words, being born in a poorer country makes a girl more likely to become a child bride, and being born into a particularly poor or rural part of that country makes child marriage more likely still. This cuts both ways: child brides in poorer regions have even fewer economic and political opportunities.
7. There are eight countries where more than half of girls marry before turning 18
Here are the eight countries where more than 50 percent of women age 20 to 24 had entered marriage as children (the metric used to determine child marriage rates) listed from those with the highest prevalence rate to the lowest: Niger, Chad, Mali, Bangladesh, Guinea, Central African Republic, Mozambique, Nepal.
As you can see, six of those eight are in sub-Saharan Africa. The prevalence rate in Niger is 75 percent, suggesting that three in four girls there can expect to be married before turning 18.
8. One in seven girls in the developing world is married before turning 15
These girls – and they are, make no mistake, children – tend to be in West and Central Africa as well as South Asia. But the developing world is huge, including billions of people (precisely how many depends on how you measure it). And that population is expected to grow rapidly, far outpacing the rest of the world. See chart 5 on this page to get a sense of its rapid, and accelerating, growth.
There are 40 countries, mostly in Africa and South Asia, where at least 30 percent of girls marry before turning 18.
9. The issue is controversial in some countries, more accepted in others
In Yemen, for example, girls often have few rights, legal protections or social norms on their side. When an 11-year-old Yemeni child bride who had been raped by her husband was brave enough to seek a divorce, the judge told her only, "We don’t divorce little girls."
In Nigeria, however, while child marriage is common in the country's Muslim-majority north, it is more controversial in the Christian-dominated south and has become a national issue. Some legislators recently tried to amend the country's constitution, to remove a provision that explicitly allows child marriages. Their effort was blocked by a coalition of 40 pro-child bride lawmakers, including one legislator who in 2010 paid a $100,000 dowry for the privilege of marrying a 13-year-old girl.
Still, at least the issue is being debated in Nigeria. That's a small step toward dealing with the underlying problem, which goes deeper than any religious or cultural norms that might say it's okay for a middle-aged man to exchange money for the marriage of a girl too young to consent. As Lauren Wolfe, of the Women Under Siege project, put it to my colleague, "Girls are the world’s forgotten population."