The number of women dying from pregnancy and childbirth has dropped sharply in the last two decades, according to a report by a consortium of United Nations agencies set to be released on Wednesday.

Maternal deaths fell to about 287,000 in 2010, the report said. The decline is attributable to increases in contraception and in antiretroviral drugs for mothers with AIDS, and to greater numbers of births attended by nurses, doctors or midwives with medical training.

The agencies said the deaths had fallen by 47 percent from the United Nations’ 1990 estimate of 543,000, but the organization has been revising its historical estimates in response to skeptical research by a rival group of epidemiologists at the University of Washington.

Two years ago, that group, the Institute for Health Metrics and Evaluation, which was founded by the Bill and Melinda Gates Foundation as a sort of check on the World Health Organization, contradicted a long-held United Nations finding that maternal deaths had remained stubbornly above 500,000 a year.

In a widely publicized study in the journal The Lancet in April 2010, the institute estimated that 343,000 maternal deaths took place in 2008. It used three times as much data from census and death records, scientific studies and other sources as previous United Nations reports had.

In response, five months later, the United Nations said it had “revised and improved” its own statistics and concluded that there were 358,000 deaths in 2008.

“When they saw our results, they changed their strategy,” said Dr. Rafael Lozano, an epidemiologist at the institute.

Last fall, the institute estimated that deaths would fall to 274,000 in 2011. The new United Nations estimate of 287,000 is within the same statistical boundaries, Dr. Lozano said.

The United Nations report also concludes that deaths are falling quickly in East Asia but slowly in Africa.

The Asian reduction is attributed largely to China, which has a one-child policy, a very high use of contraceptives and a health care system that is improving as the nation gets richer.

Southern African countries have seen the beginnings of a reversal, according to the United Nations report, which was compiled by the World Health Organization, the United Nations Children’s Fund, the United Nations Population Fund, the United Nations Population Division, the World Bank and a team from the University of California, Berkeley. A decade ago, maternal deaths in southern Africa were rising because of AIDS. As more women get drugs that restore their immune systems, deaths are dropping.

Just two countries, India and Nigeria, account for one-third of the world’s maternal deaths. Others with very high numbers include the Democratic Republic of Congo, Pakistan, Sudan, Indonesia, Ethiopia, Tanzania, Bangladesh and Afghanistan.

“There were rumors at a U.N. conference last fall that the new numbers would be in the 200,000s,” said Christy Turlington Burns, a former fashion model who founded Every Mother Counts to fight global maternal mortality after she nearly died in childbirth.

“I’m delighted to see them come down,” she added after speaking at a health conference in New York on Tuesday. “It didn’t do any good when different reports diverged by 100,000 — or when the drop seemed so rapid. That sent a message that it’s easier to save lives than it is.”

###

By DONALD G. McNEIL Jr.