Every day, around the world, more than 20,000 children are getting married, underage and illegally.

New statistics show that in countries where there are laws restricting the practice, 7.5 million girls every year are married below the minimum age permitted, according to analysis by the World Bank and Save the Children, reports The Guardian.

One in every three girls in the developing world marry before the age of 18.

Child brides often drop out of school, due to domestic responsibilities, pregnancy, parenting and social pressure and some governments, such as Tanzania, prevent married or pregnant girls from attending school.

The past two years have brought some progress. Of the 112 countries examined in the study, a total of 10 – including Costa Rica, Guatemala, Mexico and Zimbabwe – have altered their child marriage laws, either by raising the legal age of marriage or eliminating legal exceptions to the practice, such as parental or court consent.

When a girl gets married too young, her role as a wife and mother takes over, and she is more likely to leave school

Kirsty McNeill, Save the Children

In Bangladesh, however, which has one of the highest rates of child marriage in the world, the minimum age for legal exceptions was reduced.

Two-thirds of underage marriages are taking place in countries where it is legally banned, suggesting laws are not enforced. In some countries, the minimum age for marriage is lower under religious or customary law than national law, which undermines legal protection.

The study, to mark International Day of the Girl, calls for urgent action at national and international level.

Kirsty McNeill, Save the Children’s policy, advocacy and campaigns executive director said: ‘We will not see a world where girls and boys have the same opportunities to succeed in life until we eradicate child marriage. When a girl gets married too young, her role as a wife and a mother takes over. She is more likely to leave school, she may become pregnant and suffer abuse.’

‘Laws banning the practice are an important first step. But millions of vulnerable girls will continue to be at risk unless child marriage is tackled head on. We need to change attitudes in communities so that we can end this harmful practice once and for all.’

The findings come ahead of an African-led conference on ending child marriage to take place in Senegal later this month. In west Africa alone, 1.7 million girls are married below the minimum legal age every year, one of the highest rates globally.

The study estimates 100 million girls are not protected by child marriage laws.