Around 303,000 women died of complications during pregnancy or up to six weeks after giving birth in 2015 - down from 532,000 in 1990.
Officials from the World Health Organisation (WHO) said the results showed "huge progress".
However, only nine countries hit targets set by the UN.
"This report will show that by the end of 2015 maternal mortality will have dropped by 44% from its levels from 1990," said Dr Lale Say, coordinator for reproductive health and research at the WHO.
But she warned that the progress was "uneven" - with 99% of deaths happening in developing countries.
While 39 countries reported "significant progress" in reducing pregnancy-related deaths, only nine countries achieved their targets.
"Many countries with high maternal death rates will make little progress, or will fall behind, over the next 15 years if we don't improve the current number of available midwives and other health workers with midwifery skills," said Dr Babatunde Osotimehin, executive director of the UN Population Fund.
Eastern Asia saw the greatest improvement, with maternal mortality falling from approximately 95 to 27 per 100,000 live births.
The UN now aims to reduce the global ratio to less than 70 per 100,000 by 2030.