"Globally, more than 500,000 women die each year because of complications related to pregnancy and childbirth," UNICEF said in its Progress for Children report based on surveys carried out between 2005 and 2007.
More than 99 percent of all maternal deaths occur in developing countries, with some 84 percent concentrated in sub-Saharan Africa and south Asia, UNICEF said.
In the developing world, the risk of death from complications relating to pregnancy and childbirth over the course of a woman's lifetime is 1 in 17, against just 1 in 8,000 in industrialised countries.
The riskiest place to give birth is the west African country of Niger, where the risk is estimated at 1 in 7.
Moreover, for every one woman who dies, another 20 will suffer severe disability for the rest of her life such as fistula which can damage reproductive organs, or severe anaemia, said Tessa Wardlaw, the organisation's chief of statistics and monitoring.
"A maternal death is really the tip of the iceberg," she said.
UNICEF stressed that most maternal deaths are avoidable and that a key way of improving the situation is better health care such as pre- and post-natal care, family planning and HIV testing.
But Peter Salama, UNICEF's chief of health, said the issue could not be dissociated from women's overall position in society.
"There's no doubt the factors that affect women's rights in countries, whether it's early child marriage, female genital mutilation, attitudes to sexuality, have an impact on women's health," he said.
"Maternal mortality and child mortality do not yet receive the attention that the scale of the problem deserves," he added.