Some of the major health problems faced by women in developing countries are caused by "terrible" traditions that must be stopped, said the head of public health at the World Health Organisation (WHO).

Traditions such as child marriage or female genital mutilation (FGM), widely practised in some communities, contribute to high maternal mortality rates in some poor countries where girls as young as 13 get married and give birth.

Tackling traditions that can be detrimental to health and backing those changes by legislation are essential to protecting women and girls, Maria Neira told the Thomson Reuters Foundation.

"A tradition that forces a girl to get married at 13 is a bad tradition," Neira said on the sidelines of a London event on maternal mortality and access to water and sanitation. "It's time to fight all of those traditions."

Customs like child marriage mean that teenage girls get pregnant and give birth, often before their bodies are ready, and often in clinics without basic facilities like clean water or toilets.

Nearly 16 million adolescent girls give birth every year and at least 70,000 girls die each year due to pregnancy and childbirth complications, according to UNICEF.

Although maternal mortality worldwide has dropped by 50 percent in the last two decades, 289,000 women died from complications related to pregnancy and childbirth in 2013, the majority of them in developing countries, according to WHO.

Education is key to giving women a voice and empowering them to speak up for their rights, said Neira. "As soon as (women) get a minimum of education, their voice is stronger," she said.

It's also the role of global institutions, including WHO, to help women fight for their rights, she said.

"We need to focus on women because they don't have yet the power to fight for themselves. We need to empower them."