Summit on global family planning
World health leaders should address "culture as well as condoms" when they meet to discuss enhancing family planning services in the developing world, a charity said.
Cultural practices and attitudes are as big a barrier to women and girls trying to access contraception as their availability or affordability, Save the Children said.
Delegates at the London Family Planning Summit must address how to empower girls to prevent early pregnancy, the charity said.
Save the Children chief executive Justin Forsyth said: "Too often girls in the developing world want to get pregnant because they feel they have no other option in life but early motherhood.
"But pregnancy for a young girl can be a matter of life and death. More teenage girls are killed in pregnancy and childbirth than anything else. This is a global scandal.
"World leaders in London today must focus on both culture and condoms. All too often, girls are given no other option but to get pregnant - but their bodies are simply not ready to deliver a baby safely."
The charity said 75% of the 18 million adolescent pregnancies every year are intended and planned.
While richer countries are expected to pour cash into developing family planning strategies at the summit, poorer countries are expected to make policy commitments.
The White Ribbon Alliance for Safe Motherhood (WRA) said it will make sure that policy pledges made by political leaders at the summit are upheld.
WRA policy and advocacy co-ordinator Maeve Shearlaw said: "It is global scandal and violation of human rights that in many parts of the world becoming a mother is not a matter of choice for many women and girls."