While maternal mortality rates across the globe have decreased by nearly half in the last 25 years, the United States is one of 13 countries where the rate has risen, according to a new survey (PDF) published Thursday by the United Nations and World Bank.

The rate of women dying during childbirth has declined globally by 43 percent since 1990, when U.N. member states launched a series of pledges called the Millennium Development Goals aimed at making significant improvements in global indicators.

A survey led by the U.N.’s World Health Organization estimates there were 303,000 maternal deaths globally in 2015, down from 532,000 in 1990. Over the same period, the approximate global lifetime risk of maternal death fell from 1 in 180 mothers to 1 in 73.

But in the U.S., the rate of mothers dying in childbirth rose from 12 out of 100,000 births to 14 in the years from 1990 to 2015.

By comparison, the same rate in Sweden, Switzerland, Spain, Norway, Italy, Iceland, Greece and Kuwait has remained below 10 in 100,000 births for the last 25 years. And Canada’s rate is about half that of the U.S.

William Heisel, director of global engagement for the Institute of Health Metrics and Evaluation, an independent research center at the University of Washington, said several factors help to explain why the U.S. has more women dying in childbirth — including higher rates of obesity, diabetes and other conditions that can complicate pregnancies.

“We don’t do as well as many high-income countries on a whole range of health outcomes,” said Heisel of the U.S rates.

Underpinning the U.S. increase in the number of women dying in childbirth are the country’s racial disparities and health care gaps, studies have shown.

Black women in the U.S. died in childbirth at a rate three times higher than white women in 2011, according to the Centers for Disease Control and Prevention.

Heisel also said the U.S. tends to reward specialists within the health care system, rather than putting a high value on primary care, with a resulting adverse affect on maternity care.

“When you’re a woman who’s pregnant, when you’re getting regular care and attention form your physician … that pays off."