Story highlights UNICEF releases estimates that child marriages are falling

While they're declining in South Asia, shift is to sub-Saharan Africa

(CNN) Child marriages are declining, with the largest drop in South Asia, according to UNICEF.

Ten years ago, a South Asian girl's risk of getting married as a child was about 50%, but now that has fallen to about 30%. A UNICEF release Tuesda y attributed the progress in India to increasing rates of girls' education, government investments and public messaging around the illegality of child marriage.

"Any reduction is welcome news, but we've got a long way to go," said Anju Malhotra, UNICEF's principal gender adviser.

Even with the declines, 12 million girls are married in childhood every year, according to UNICEF.

Globally, one in five women are married before they turn 18 years old. A decade ago, the rate had been one in four, UNICEF said Tuesday.