The rate at which women die in childbirth or soon after delivery has fallen by about 40 percent since 1980, with dramatic reductions in the populous nations of India, China, Brazil and Egypt.

Maternal mortality is a key gauge of a population's health and wealth, as well as of women's status. The rate differs greatly between countries and regions, with the best- and worst-performing nations differing by a factor of about 400, according to a study in the Lancet, a European medical journal.

The global rate in 2008 was 251 maternal deaths for every 100,000 live births, according to a research team led by Christopher Murray at the University of Washington. The highest rate was in Afghanistan (1,575) and the lowest in Italy (4). The United States was 17, Canada 7 and Mexico 52.

More than half of all maternal deaths (about 343,000 in 2008) occurred in only six countries, researchers found: India, Nigeria, Pakistan, Afghanistan, Ethiopia and the Democratic Republic of the Congo.

Between 1980 and 2008, China's maternal mortality rate fell from 165 to 40; India's from 677 to 254; and Brazil's from 149 to 55. In many sub-Saharan African countries, a decline that began in the 1980s flattened out in the 1990s because of the prevalence of HIV infection, which increases a woman's risk of death during pregnancy and after delivery.

Prenatal care and "skilled birth attendants" - midwives or physicians - at delivery reduce both a woman's and her baby's risk of dying in childbirth or soon after. Maternal mortality also tends to fall when per capita income rises, when women have fewer children, and when they go to school longer.

Maternal and child health - partly eclipsed by AIDS, tuberculosis and malaria in the past decade - is gaining attention on the global health agenda. It is a major part of the Obama administration's Global Health Initiative. Norway is devoting about 35 percent of its overseas development aid to maternal, newborn and child health.

A group of public health experts - joined by six government leaders in the United States for this week's Nuclear Security Summit - will meet in New York City this week to map a strategy for further reducing maternal and child mortality.

They are two of the eight Millennium Development Goals established by the United Nations in 2000.

"We do not have silver bullets for achieving this," said Flavia Bustreo, an Italian physician who directs a partnership, headquartered in Geneva, of 300 health organizations. Instead, she said, there is a menu of proven interventions that need to be implemented more widely.

For example, in the 68 countries where 97 percent of maternal deaths occur, less than 20 percent of recently delivered women are visited at home by a health worker who can instruct in breast-feeding and assess the mother and infant for infection. Only 50 percent of deliveries in those countries have skilled birth attendants present. On the other hand, more than 80 percent of babies get the recommended immunizations.