The researchers said on Monday their findings show it is possible to save women's lives if countries want to and said their analysis should point to ways to do so.
The AIDS pandemic alone, they said, killed more than 61,000 women in and around the time of childbirth in 2008, most of them in Africa.
"These findings are very encouraging and quite surprising. There are still too many mothers dying worldwide, but now we have a greater reason for optimism than has generally been perceived," said Dr. Christopher Murray of the Institute for Health Metrics and Evaluation at the University of Washington, who led the study.
The findings contradict work done by the World Health Organization, which reported last May that mothers and newborns are no more likely to survive now than 20 years ago.
Murray and colleagues took every bit of data they could find on deaths of women from records in 181 countries and plugged this information into a computer model.
"We estimated that there were 342,900 deaths worldwide in 2008, down from 526,300 in 1980," they wrote in their report, published in the Lancet medical journal.
They found the number of women dying from pregnancy-related causes has dropped by more than 35 percent globally in the past 30 years.
"One of the most surprising results is the apparent rise in the maternal mortality rate in the USA, Canada, and Norway," they added. But it can partly be because US death certificates recently started asking about pregnancy, they added.
But this does not explain why US maternal deaths are double the rates in Britain, triple the rates in Australia and four times the rate in Italy, they said.
In the United States the rate rose from 12 deaths per 100,000 live births in 1980 to 17 in 2008. In Canada, the rate hovered between 6 and 7 for the whole time and Norway's rose from 7 per 100,000 in 1980 to 8 per 100,000 in 2008.
The United States is currently embroiled in reforming its healthcare system, where more is spent per capita than in comparable developed countries but with poorer results, as demonstrated by maternal and newborn death rates and high rates of diabetes and heart disease.
China, Egypt, Ecuador and Bolivia made some of the most progress in lowering maternal death rates, Murray's team found.
In China, the rate fell from 165 per 100,000 to 40 per 100,000.
"Progress overall would have been greater if the HIV epidemic had not contributed to substantial increases in maternal mortality in eastern and southern Africa," they added.
Nearly one out of every five maternal deaths or a total of 61,400 in 2008, were associated with AIDS infections.
About 80 percent of all deaths of pregnant women or new mothers were in 21 countries, with half of all such deaths in just six countries - India, Nigeria, Pakistan, Afghanistan, Ethiopia, and the Democratic Republic of the Congo.
"Finding out why a country such as Egypt has had such enormous success in driving down the number of women dying from pregnancy-related causes could enable us to export that success to countries that have been lagging behind," Murray said.
