"U.S. law and U.S. Department of State policy aim to prevent and reduce the risks of child marriages occurring around the world, yet major loopholes in U.S. law have allowed thousands of minors to be subjected to child marriages. Under the 'Immigration and Nationality Act' ('INA'), a U.S. child may petition for a visa for a spouse or fiancé living in another country, and a U.S. adult may petition for a visa for a minor spouse or fiancé living abroad. [...] Over the last eleven years (FY2007 to FY2017), USCIS [U.S. Customs and Immigration Services] approved 3,595,447 petitions for spousal or fiancé entry in to the United States. Of those, 8,686 involved a minor. Two minors whose petitions were approved were 13 years old; 38 were 14 years old; 269 were 15 years old; 1,768 were 16 years old; and the remaining 6,609 were 17 years old. Girls were the younger party in 95 percent of the petitions approved by USCIS."
United States Senate, Committee on Homeland Security and Governmental Affairs: https://www.hsgac.senate.gov/