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Merck & Co on Tuesday said it is expanding its "Merck for Mothers" program, which aims to reduce pregnancy-related deaths from impoverished countries such as Senegal and Zambia, to the United States - a stark reminder of how far the country lags other wealthy nations on key measures of health.

"As Americans, we simply should not accept that 46 countries have lower rates" of reported maternal mortality, said Merck Chief Executive Ken Frazier. The fact that U.S. pregnancy-related deaths have nearly doubled since 1990 is "appalling" and "something we ought to be ashamed of," he said.

"Given how sophisticated medical care is in this country, I think most Americans would be astonished" that almost 900 women die each year as a result of pregnancy or childbirth and 50,000 have close calls, Frazier said.

The U.S. drugmaker launched the $500 million global program in 2011 to reduce pregnancy-related deaths, focusing on India, Uganda and other poor countries with only rudimentary healthcare systems.

However, pregnancy-related deaths in the United States have risen from 7.2 per 100,000 live births in 1987 to 17.8 per 100,000 in 2009 (the latest year with reliable data), according to the U.S. Centers for Disease Control and Prevention. The rate among African-American women is more than triple that of white women: 35.6 versus 11.7 deaths per 100,000 live births.

The deaths include any that occur while a woman is pregnant or within a year after she gives birth, from any cause related to or aggravated by pregnancy.

The leading maternal killers include cardiovascular disease, venous thromboembolism, hemorrhage, hypertension and sepsis, said Dr Mary D'Alton of Columbia University Medical Center in New York City, a specialist in high-risk maternal and fetal medicine.

According to a study presented on Sunday at a meeting of the American Heart Association, heart disease is the leading cause of pregnancy-related deaths in California. "Women who give birth are usually young and in good health," said Dr Afshan Hameed of the University of California, Irvine, who led the research. "So heart disease shouldn't be the leading cause of pregnancy-related deaths, but it is."

The reasons for the rise in maternal mortality are unclear. Better reporting is part of it: some states only recently added a "pregnancy" check box to death certificates, said Dr Edward McCabe, medical director of the March of Dimes.

"We're getting better data, yes, but what these data are telling us is that we have an unacceptably high rate of pregnancy-related mortality."

Another likely reason for the increase is the rising prevalence of chronic diseases. Diabetes, chronic heart disease and hypertension - which can occur as a result of obesity - have become more common in women of reproductive age. And for unexplained reasons, the 2009 H1N1 (swine flu) pandemic killed many pregnant women in the United States: although pregnant women account for about 1 percent of the U.S. population, they made up 5 percent of the deaths, the CDC reported.

"Merck for Mothers" will provide $6 million to U.S. programs in 10 states and three cities aimed at decreasing the number of women who die as a result of being pregnant or giving birth. Local programs include Baltimore Healthy Start, which works with neighborhood clinics to improve prenatal and primary care for pregnant women who have high-blood pressure, diabetes and other chronic conditions, and the Maternity Care Coalition in Philadelphia, whose "Safe Start MOMobile" sends health advocates into the homes of high-risk pregnant women.

The program will also work through the American Congress of Obstetricians and Gynecologists to develop standardized protocols for treating the leading causes of maternal death, said Columbia's D'Alton. Currently, there is significant variation in how obstetricians and hospitals treat potentially-fatal obstetric emergencies such as postpartum hemorrhaging and embolisms.

"There are no national guidelines about what to do in the event of a maternal emergency," D'Alton said. "Variability is the enemy of safety."

Merck is collaborating with the London School of Hygiene & Tropical Medicine to assess whether its maternity programs in Uganda, Zambia and other countries are making a difference, and will publish data on what works and what doesn't.